半干旱黄土区集雨措施和养分添加对苜蓿草地和封育植被生产力及土壤生态化学计量特征的影响
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摘要
本文以半干旱黄土高原地区(甘肃省榆中县北山地区)利用垄沟集雨技术建成的人工苜蓿草地和围栏封育的撂荒地演替植被为对象,通过2年的大田试验研究了垄沟集雨技术下的苜蓿草地干草产量、水分利用效率、土壤剖面水分动态、苜蓿根系及地上凋落物的分解特征与养分动态、分解速率对集雨技术的响应及土壤生态化学计量特征；初步探讨了养分添加对封育的撂荒地演替植被地上生物量、地下生物量、根冠比的影响；以及养分添加对封育植被土壤生态化学计量特征的影响和植被建设的作用。为此,我们在榆中县北山地区进行了四个实验。实验一：垄沟集雨对紫花苜蓿人工草地土壤水分和产草量的影响,实验设5个处理：1)CK：常规平作,不起垄,不覆膜(对照)；2)M30：垄和沟的宽度都为30 cm,垄上覆盖塑料薄膜；3)M60.垄和沟的宽度都为60 cm,垄上覆盖塑料薄膜；4)B30：垄和沟的宽度都为30 cm,不覆膜；5)B60：垄和沟的宽度都为60 cm,不覆膜。实验二：苜蓿根系和地上凋落物野外埋置分解试验,实验在实验一的5个处理中进行野外分解。实验三：集雨措施对植株残体和根系,有机肥野外埋置分解的影响,实验设2个处理：1)F：平地不起垄,不覆膜；2)H：起垄覆膜,垄和沟宽都为60cm。实验四：养分添加对围栏封育的撂荒地植被土壤生态化学计量特征的影响和植被建设的作用,实验设4个处理：1)CK：不施肥(对照)；2)N：只添加氮肥；3)P：只添加磷肥；4)NP：同时添加氮肥和磷肥。主要实验结果如下：
实验一：1)垄沟覆膜处理(M60)能显著提高苜蓿干草产量,裸露处理(B30、B60)的苜蓿干草产量反而降低,各处理之间的产量关系为：M60>M30>CK>B60>B30,这一产量的大小顺序与前七年是保持一致的；M60能提高水分利用效率；此外,M60处理在高产的同时保证了浅层(0-100cm)土壤的水分补充。2)种植苜蓿能有效提高0-20cm土层的土壤有机质含量；种植苜蓿会导致0-20cm的土壤C/N比降低,C/N比减小将导致土壤有机质分解加速,导致土壤有机质降低,在本研究中,M60处理能很好的减缓0-20cm土壤C/N的降低。
实验二：1)苜蓿根系分解速率(K)大于地上凋落物：KM60R(0.0029)>KM60L(0.0021)、KM30R(0.0025)> KM30L(0.0012)、KB60R(0.0025)> KB60L(0.0014)、KB30R(0.0023)> KB30L(0.0014)、KCKR(0.0022)>KCJL(0.0014);苜蓿地上凋落物的分解速率与凋落物的初始N含量、C/P显著正相关,而与初始C/N显著负相关。2)苜蓿根系和地上凋落物野外埋置分解的前90d植物有机碳迅速释放,有机碳含量较分解前显著降低,随后释放减缓,分解450d后, M60处理的地上凋落物有机碳释放量最大(81.0g/kg)。所有处理的苜蓿根系和地上凋落物在埋置分解450d后,分解残体的全N(B30除外)、全P均较基底值(分解前的值)增加,表现为N、P素的富集积累。3)分解袋野外埋置分解450d后,苜蓿根系和地上凋落物的C/N比均显著降低,对于根系残体,其C/N比降低幅度的大小依次为：M30(9.70)>M60(9.48)>CK(9.27)>B60(8.41)>B30(7.24);而对于地上凋落物,其C/N比降低幅度依次是CK(9.59)>M30(9.27)>B30(7.91)>M60(7.69)>B60(5.69)。4)分解速率除了与底物自身化学组成密切相关外,还受环境因子影响,本实验发现苜蓿根系及地上凋落物的分解速率与0-20cm土层的土壤水分呈正相关(p<0.05)。5)分解袋野外埋置分解450d后,残体附近2-3cm的0-20cm土层的土壤有机质(SOC)含量都增加了,且根系分解残体0-20cm的SOC含量高于地上凋落物分解残体的SOC含量；分解过程中残体附近2-3cm的0-20cm土层的土壤C/N比随分解时间增加而增大,其中M60处理的根系分解450d后残体的土壤C/N比最大(9.20),CK与M30的地上凋落物分解的土壤C/N比最小(8.50),此外,根系残体附近2-3cm的0-20cm土层的土壤C/N比都大于地上凋落物残体0-20cm土壤C/N比(B30处理除外)。6)分解袋野外埋置分解450d后,根系残体附近2-3cm的0-20cm土层的土壤速效磷趋势为：裸露处理>CK>覆膜处理,且M60处理最低,而地上凋落物残体0-20cm的土壤速效磷含量依次为：B30 (5.54mg/kg)∽CK (5.33mg/kg)∽B60 (5.29mg/kg)>M30 (4.43mg/kg)>M60 (3.66mg/kg);分解450d后,根系残体附近2-3cm的0-20cm土层的土壤C/P比大于地上凋落物残体0-20cm的土壤C/P比,覆膜处理残体附近2-3cm的0-20cm土壤C/P比大于裸露处理和对照CK,其中M60处理的C/P比最大,CK处理的C/P比最小。
实验三：小麦、玉米、豌豆、苜蓿、土豆等五种作物植株残体和根系及有机肥在垄沟覆膜集雨处理下的分解速率大于平地不覆膜处理,实验还发现,野外埋置的分解速率与0-20cm土壤含水量呈正相关。
实验四：添加N肥、P肥能够增加围栏封育撂荒地植被整个生长季的地上生物量,且添加P肥处理的地上生物量为四个处理中最高,但添加NP肥处理的地上生物量和对照无显著差异；添加N肥会加剧土壤水分消耗,而添加P肥、NP则有利于土壤水分的恢复。实验还发现,添加N肥会使0-20cm土层的SOC含量降低,同时0-20cm的土壤C/N比降低,而添加P肥、NP肥能有效提高0-20cm土层的SOC和土壤全氮含量,并且能缓解0-20cm土壤C/N比的降低。因此,综合考虑生产效益和生态利益,添加P肥有利于围栏封育撂荒植被的恢复和建设。
We evaluated the effect of ridge and furrow rainfall harvesting technique on alfalfa grassland yield, water use efficiency, profile soil water dynamics, soil nutrient dynamics and the decomposition feature of alfalfa root and litter, and the soil ecological stoichiometry feature by 2 years field experiment in the semi-arid Loess Plateau (Beishan of Yuzhong County, Gansu Province). We also assessed the influence of nutrient applying on fenced natural vegetation aboveground biomass, belowground biomass, root/shoot ratio, the soil ecological stoichiometry feature, and the effect of nutrient applying on vegetation establishment. To this end, four experiments had been conducted in Beishan of Yuzhong County. In the First experiment, five treatments were used:1) CK:Conventional cultivation in flat treatment without mulch; 2) M30: Plastic mulched ridge with the width of ridge and furrow as 30cm; 3) M60:Plastic mulched ridge with the width of ridge and furrow as 60cm; 4) B30:Bare ridge with width of ridge and furrow 30cm; 5) B60:Bare ridge with width of ridge and furrow 60cm. The second experiment: Alfalfa root and shoot litter decomposition embedded field test. There were also five treatments as to the first. The third experiment:the effect of ridge and furrow rainfall harvesting technique on the decomposition of five crops residue, roots and organic fertilizer:it had tow treatments:1) F:Flat treatment without mulch; 2) H:Plastic mulched ridge with the width of ridge and furrow as 60cm. There were four treatments in the last-the effect of nutrient applying on the soil ecological stoichiometry and vegetation establishment:1) CK:Contrast, no fertilizer; 2) N:Add nitrogen fertilizer; 3) P:Add phosphate fertilizer; 4) NP:Add nitrogen+phosphate fertilizer. The main results as below:
1. The first Experiment:1) M60 has been proved to be the effective way of increasing alfalfa production, while B30 and B60 have a negative effect in 2008 and 2009. The order of production on different water harvesting regimes was M60>M30>CK>B60>B30, which was the same as the results of seven years ago. M60 had a higher WUE rather than
higher water consumption, besides, M60 had a positive effect of water complement on soil 0-100cm layer.2) Alfalfa cultivation can enhance soil organic matter in the 0-20cm layer of soil. Even though it can reduce C/N, which means the acceleration of decomposition of SOC and decrease SOC content, in our experiment M60 play a better role on decreasing C/N.
2. The second Experiment:1) Decomposition rate (K) of alfalfa root was higher than litter: KM60R(0.0029)> KM60L(0.0021), KM30R(0.0025)> KM30L(0.0012), KB60R(0.0025)> KB60L(0.0014), KB30R(0.0023)> KB30L(0.0014), KCKR(0.0022)> KCKL(0.0014). The decomposition rate of litter has a significantly positive correlation with its initial nitrogen content and C/P ratio, while it has a significantly negative correlation with its initial C/N ratio.2) In the field, roots and litters released more organic carbon (SOC was significantly lower than before decomposition) in the former 90ds, then slowly. The alfalfa litter in M60 has the highest organic carbon release, which was 81.0g/kg. The soil total nitrogen (exclude B30) and soil total phosphorus content increased in all root and litter decomposition treatments than before after 450ds. It showed nutrient enrichment in the soil.3) Alfalfa root and litter C/N ratio decreased significantly than initial value after decomposition. The order of C/N ratio decrease in different ridge and furrow rainfall harvesting technique was M30 (9.7)>M60 (9.48)>CK (9.27)>B60 (8.41)>B30 (7.24) for alfalfa root, while it was CK (9.59)>M30 (9.27)> B30 (7.91)> M30 (7.69)> B60 (5.69) for alfalfa litter.4) Decomposition rate is closely related to its chemical composition and affected by environmental factors. We found the decomposition rate of alfalfa root and litter had a significantly positive correlation with soil water content in the 0-20cm layer.5) SOC increased in different extent after 450ds decomposition of alfalfa root and litter in the field, which is in the 0-20cm layer soli of residue near 2-3cm. Furthermore, SOC from alfalfa root was more than it from litter. The soil C/N ratio has increased along the time goes. M60 has the highest C/N ratio (9.20) after alfalfa root decomposition while CK and M30 have the lowest C/N ratio (8.50) after alfalfa litter decomposition. Besides, soil C/N ratio after alfalfa root decomposition was higher than it after litter decomposition. The soil available phosphorus content differed in different treatments after 450ds decomposition, which was bare soil treatments> CK> film mulched treatments and M60 has the lowest soil available phosphorus content. The soil available phosphorus from alfalfa litter was 5.54mg/kg in B30, 5.53mg/kg in CK,5.29mg/kg in B60,4.43mg/kg in M30, and 3.66mg/kg in M60. After 450ds decomposition, C/P ratio in all treatments was higher in root than in litter and film mulched treatments> bare soil treatments and CK. M60 has the highest C/P ratio and CK has the lowest.
3. The third Experiment:The decomposition rate of wheat, maize, pea, potato and alfalfa shoot, root and manure were accelerated under ridge and furrow with film mulched rainfall harvesting technique and it was positively correlation with 0-20 cm soil water content.
4. The last Experiment:The productivity of fenced natural vegetation was enhanced by applying P fertilizer and N fertilizer, the productivity by applying P fertilizer was the highest. But applying P fertilizer can't enhance productivity. Adding N fertilizer would increase soil water consumption, and apply P, NP fertilizer can benefit the soil water. Our results showed, SOC and soil C/N ratio in the 0-20cm layer of soil were decreased by applying N fertilizer, but increased by applying P, NP fertilizer. Besides, by applying P fertilizer in restoration land could prevent C/N ratio decreasing. Thus, applying P fertilizer was an effective way for fenced vegetation to establish and restore.
实验一：1)垄沟覆膜处理(M60)能显著提高苜蓿干草产量,裸露处理(B30、B60)的苜蓿干草产量反而降低,各处理之间的产量关系为：M60>M30>CK>B60>B30,这一产量的大小顺序与前七年是保持一致的；M60能提高水分利用效率；此外,M60处理在高产的同时保证了浅层(0-100cm)土壤的水分补充。2)种植苜蓿能有效提高0-20cm土层的土壤有机质含量；种植苜蓿会导致0-20cm的土壤C/N比降低,C/N比减小将导致土壤有机质分解加速,导致土壤有机质降低,在本研究中,M60处理能很好的减缓0-20cm土壤C/N的降低。
实验二：1)苜蓿根系分解速率(K)大于地上凋落物：KM60R(0.0029)>KM60L(0.0021)、KM30R(0.0025)> KM30L(0.0012)、KB60R(0.0025)> KB60L(0.0014)、KB30R(0.0023)> KB30L(0.0014)、KCKR(0.0022)>KCJL(0.0014);苜蓿地上凋落物的分解速率与凋落物的初始N含量、C/P显著正相关,而与初始C/N显著负相关。2)苜蓿根系和地上凋落物野外埋置分解的前90d植物有机碳迅速释放,有机碳含量较分解前显著降低,随后释放减缓,分解450d后, M60处理的地上凋落物有机碳释放量最大(81.0g/kg)。所有处理的苜蓿根系和地上凋落物在埋置分解450d后,分解残体的全N(B30除外)、全P均较基底值(分解前的值)增加,表现为N、P素的富集积累。3)分解袋野外埋置分解450d后,苜蓿根系和地上凋落物的C/N比均显著降低,对于根系残体,其C/N比降低幅度的大小依次为：M30(9.70)>M60(9.48)>CK(9.27)>B60(8.41)>B30(7.24);而对于地上凋落物,其C/N比降低幅度依次是CK(9.59)>M30(9.27)>B30(7.91)>M60(7.69)>B60(5.69)。4)分解速率除了与底物自身化学组成密切相关外,还受环境因子影响,本实验发现苜蓿根系及地上凋落物的分解速率与0-20cm土层的土壤水分呈正相关(p<0.05)。5)分解袋野外埋置分解450d后,残体附近2-3cm的0-20cm土层的土壤有机质(SOC)含量都增加了,且根系分解残体0-20cm的SOC含量高于地上凋落物分解残体的SOC含量；分解过程中残体附近2-3cm的0-20cm土层的土壤C/N比随分解时间增加而增大,其中M60处理的根系分解450d后残体的土壤C/N比最大(9.20),CK与M30的地上凋落物分解的土壤C/N比最小(8.50),此外,根系残体附近2-3cm的0-20cm土层的土壤C/N比都大于地上凋落物残体0-20cm土壤C/N比(B30处理除外)。6)分解袋野外埋置分解450d后,根系残体附近2-3cm的0-20cm土层的土壤速效磷趋势为：裸露处理>CK>覆膜处理,且M60处理最低,而地上凋落物残体0-20cm的土壤速效磷含量依次为：B30 (5.54mg/kg)∽CK (5.33mg/kg)∽B60 (5.29mg/kg)>M30 (4.43mg/kg)>M60 (3.66mg/kg);分解450d后,根系残体附近2-3cm的0-20cm土层的土壤C/P比大于地上凋落物残体0-20cm的土壤C/P比,覆膜处理残体附近2-3cm的0-20cm土壤C/P比大于裸露处理和对照CK,其中M60处理的C/P比最大,CK处理的C/P比最小。
实验三：小麦、玉米、豌豆、苜蓿、土豆等五种作物植株残体和根系及有机肥在垄沟覆膜集雨处理下的分解速率大于平地不覆膜处理,实验还发现,野外埋置的分解速率与0-20cm土壤含水量呈正相关。
实验四：添加N肥、P肥能够增加围栏封育撂荒地植被整个生长季的地上生物量,且添加P肥处理的地上生物量为四个处理中最高,但添加NP肥处理的地上生物量和对照无显著差异；添加N肥会加剧土壤水分消耗,而添加P肥、NP则有利于土壤水分的恢复。实验还发现,添加N肥会使0-20cm土层的SOC含量降低,同时0-20cm的土壤C/N比降低,而添加P肥、NP肥能有效提高0-20cm土层的SOC和土壤全氮含量,并且能缓解0-20cm土壤C/N比的降低。因此,综合考虑生产效益和生态利益,添加P肥有利于围栏封育撂荒植被的恢复和建设。
We evaluated the effect of ridge and furrow rainfall harvesting technique on alfalfa grassland yield, water use efficiency, profile soil water dynamics, soil nutrient dynamics and the decomposition feature of alfalfa root and litter, and the soil ecological stoichiometry feature by 2 years field experiment in the semi-arid Loess Plateau (Beishan of Yuzhong County, Gansu Province). We also assessed the influence of nutrient applying on fenced natural vegetation aboveground biomass, belowground biomass, root/shoot ratio, the soil ecological stoichiometry feature, and the effect of nutrient applying on vegetation establishment. To this end, four experiments had been conducted in Beishan of Yuzhong County. In the First experiment, five treatments were used:1) CK:Conventional cultivation in flat treatment without mulch; 2) M30: Plastic mulched ridge with the width of ridge and furrow as 30cm; 3) M60:Plastic mulched ridge with the width of ridge and furrow as 60cm; 4) B30:Bare ridge with width of ridge and furrow 30cm; 5) B60:Bare ridge with width of ridge and furrow 60cm. The second experiment: Alfalfa root and shoot litter decomposition embedded field test. There were also five treatments as to the first. The third experiment:the effect of ridge and furrow rainfall harvesting technique on the decomposition of five crops residue, roots and organic fertilizer:it had tow treatments:1) F:Flat treatment without mulch; 2) H:Plastic mulched ridge with the width of ridge and furrow as 60cm. There were four treatments in the last-the effect of nutrient applying on the soil ecological stoichiometry and vegetation establishment:1) CK:Contrast, no fertilizer; 2) N:Add nitrogen fertilizer; 3) P:Add phosphate fertilizer; 4) NP:Add nitrogen+phosphate fertilizer. The main results as below:
1. The first Experiment:1) M60 has been proved to be the effective way of increasing alfalfa production, while B30 and B60 have a negative effect in 2008 and 2009. The order of production on different water harvesting regimes was M60>M30>CK>B60>B30, which was the same as the results of seven years ago. M60 had a higher WUE rather than
higher water consumption, besides, M60 had a positive effect of water complement on soil 0-100cm layer.2) Alfalfa cultivation can enhance soil organic matter in the 0-20cm layer of soil. Even though it can reduce C/N, which means the acceleration of decomposition of SOC and decrease SOC content, in our experiment M60 play a better role on decreasing C/N.
2. The second Experiment:1) Decomposition rate (K) of alfalfa root was higher than litter: KM60R(0.0029)> KM60L(0.0021), KM30R(0.0025)> KM30L(0.0012), KB60R(0.0025)> KB60L(0.0014), KB30R(0.0023)> KB30L(0.0014), KCKR(0.0022)> KCKL(0.0014). The decomposition rate of litter has a significantly positive correlation with its initial nitrogen content and C/P ratio, while it has a significantly negative correlation with its initial C/N ratio.2) In the field, roots and litters released more organic carbon (SOC was significantly lower than before decomposition) in the former 90ds, then slowly. The alfalfa litter in M60 has the highest organic carbon release, which was 81.0g/kg. The soil total nitrogen (exclude B30) and soil total phosphorus content increased in all root and litter decomposition treatments than before after 450ds. It showed nutrient enrichment in the soil.3) Alfalfa root and litter C/N ratio decreased significantly than initial value after decomposition. The order of C/N ratio decrease in different ridge and furrow rainfall harvesting technique was M30 (9.7)>M60 (9.48)>CK (9.27)>B60 (8.41)>B30 (7.24) for alfalfa root, while it was CK (9.59)>M30 (9.27)> B30 (7.91)> M30 (7.69)> B60 (5.69) for alfalfa litter.4) Decomposition rate is closely related to its chemical composition and affected by environmental factors. We found the decomposition rate of alfalfa root and litter had a significantly positive correlation with soil water content in the 0-20cm layer.5) SOC increased in different extent after 450ds decomposition of alfalfa root and litter in the field, which is in the 0-20cm layer soli of residue near 2-3cm. Furthermore, SOC from alfalfa root was more than it from litter. The soil C/N ratio has increased along the time goes. M60 has the highest C/N ratio (9.20) after alfalfa root decomposition while CK and M30 have the lowest C/N ratio (8.50) after alfalfa litter decomposition. Besides, soil C/N ratio after alfalfa root decomposition was higher than it after litter decomposition. The soil available phosphorus content differed in different treatments after 450ds decomposition, which was bare soil treatments> CK> film mulched treatments and M60 has the lowest soil available phosphorus content. The soil available phosphorus from alfalfa litter was 5.54mg/kg in B30, 5.53mg/kg in CK,5.29mg/kg in B60,4.43mg/kg in M30, and 3.66mg/kg in M60. After 450ds decomposition, C/P ratio in all treatments was higher in root than in litter and film mulched treatments> bare soil treatments and CK. M60 has the highest C/P ratio and CK has the lowest.
3. The third Experiment:The decomposition rate of wheat, maize, pea, potato and alfalfa shoot, root and manure were accelerated under ridge and furrow with film mulched rainfall harvesting technique and it was positively correlation with 0-20 cm soil water content.
4. The last Experiment:The productivity of fenced natural vegetation was enhanced by applying P fertilizer and N fertilizer, the productivity by applying P fertilizer was the highest. But applying P fertilizer can't enhance productivity. Adding N fertilizer would increase soil water consumption, and apply P, NP fertilizer can benefit the soil water. Our results showed, SOC and soil C/N ratio in the 0-20cm layer of soil were decreased by applying N fertilizer, but increased by applying P, NP fertilizer. Besides, by applying P fertilizer in restoration land could prevent C/N ratio decreasing. Thus, applying P fertilizer was an effective way for fenced vegetation to establish and restore.
引文
Aerts R, Caluwe HD,1997. Nutritional and plant mediated controls on leaf litter decomposition of Carex species [J]. Ecology,78(1):244-260
Aerts R, DeCaluwe H,1999. Nitrogen deposition effects on carbon dioxide and methane emissions from temperate peat land soils [J].Oikos,84:44-54
Anderson JPE, Domsch KH,1980. Quantities of plant nutrients in the microbial biomass of selected soil [J]. Soil Sci,30:211-216
Bauder JW, Bauder A, Ramirez JM, Cassel DK,1987. Alfalfa water use and production on dry land and irrigated sandy loam [J]. Agronomy Journal,70:95-99
Blad BL, Rosenberg NJ,1976. Evaluation of resistance and mass transport evapotmnspiration models requiring canopy temperature data [J]. Agronomy Journd,68:764-769
Campbell CA, Biederbeck VO, Zenter RP, et al.,1991. Effect of crop rotation and cultural practices on soil organic matter, microbial biomass and respiration in a thin black chernozem [J]. Can J Soil Sci, 71:363-376
Chapin SF Ⅲ, Matson P, Mooney HA.2002. Principles of terrestrial ecosystem ecology [M]. Springer-Verlag, New York, Inc
Chen H, Harmon ME, Griffiths PR, et al.,2001. Effects of temperature and moisture on C respired from decomposing woody roots [J]. Forest Ecology and Management,138:51-64
Cotrufo MF, Inescon P,1996. Elevated CO2 reduces field decomposition rates of Betula pendula Roth. Leaf litter [J]. Oecologia,106:525-530
Disc NB, Matzner E, Forsius M,1998. Evaluation of organic horizon C:N ratio as an indicator of nitrate leaching in conifer forests across Europe [J]. Environmental Pollution,102(S1):453-456
Elser JJ, Dobberfuhl D, MacKay NA, Schampel J H,1996. Organism size, life history, and N:P stoichiometry:Towards a unified view of cellular and ecosystem processes [J]. BioScience,46:674-684
Elser JJ, Sterner RW, Gorokhova E, Fagan WF, Markow TA, Cotner JB, Harrison J F, Hobbie SE, Odell GM, Weider LW,2000b. Biological stoichiometry from genes to ecosystems [J]. Ecology Letters,3:540-550
Enriquez S, Duarte CM, Jensen, K,1993. Patterns in decomposition rates among photosynthetic organisms: the importance of detritus C:N:P content [J], Oecologia,94:457-471
Gathumbi SM, Bohlen PJ, Graetz DA,2005. Nutrient Enrichment of Wetland Vegetation and Sediments in Subtropical Pastures [J]. Soil Sci. Soc. Am. J.69:539-548
Gijsman AJ, Alarcon HF, Thomas RJ,1997. Root decomposition in tropical grasses and legumes as affected by soil texture and season. Soil Biol Biochem,29:1443-1450
Gundersen P, Callesen I, de Vries W.1998. Nitrate leaching in forest ecosystems is controlled by forest floor C/N ratio [J]. Environmental Pollution,102:403-407
Hessen DO,1997. Stoichiometry in food webs-Lotka revisited [J].Oikos,79,195-200
Hobbie SE,1996. Temperature and plant species control over litter decomposition in Alaskan tundra [J]. Ecol Monog,66:503-522
Jia Yu, Li FM, Wang XL, Xu JZ,2006. Dynamics of soil organic carbon and soil fertility affected by alfalfa productivity in a semiarid agro-ecosystem [J]. Biogeochemistry,80:233-243
Jiang HM, Jiang JP, Jia Y, Li FM, Xu JZ.2006. Soil carbon pool and effects of soil fertility in seeded alfalfa fields on the semi-arid Loess Plateau in China [J]. Soil Biology & Biochemistry,38:2350-2358
Kemp P R, Deborah GW, Clenton EO, James FR, Ross AV,1994. Effects of elevated CO2 and nitrogen fertilization pretreatments on decomposition on tallgrass prairie leaf litter [J]. Plant Soil,165:115-127
Koukoura Z,1998. Decomposition and nutrient release from C3 and C4 plant litters in a natural grassland [J]. Acta Oecol,19(2):115-123
Krogman KK, Hobbs EH,1965. Evapotranspiration of irrigated alfalfa as related to season and growth stage [J]. Canadian, Journal of Plant Science,45:310-313
Li FM, Song QH, Jjemba PK, Shi YC,2004. Dynamics of soil microbial biomass C and soil fertility in cropland mulched with plastic film in a semiarid agro-ecosystem [J]. Soil Biology & Biochemistry. 36:1893-1902
Li FM, Wang TC, Cao J,1998. Effect of organic matter on total amount and availability of nitrogen and phosphorus in Loess soil of Northwest China [J]. Communications in Soil Science and Plant Analysis. 29:947-953
Li FM, Xu JZ, Sun GJ,2003.Restoration of degraded ecosystems and development of water harvesting ecological agriculture in the semiarid Loess Plateau of China [J]. Acta Ecol Sin,23 (9):1901-1909
Lisa CW, Sebastien PCR, Ribriowx, et al.,2001. Phosphate availability regulates root system architecture in Arabidopsis [J]. Plant Physiol,126:875-882
Liu P, Huang JH, Han XG, Sun OJ, Zhou ZhY,2006. Differential responses of litter decomposition to increased soil nutrients and water between two contrasting grassland plant species of Inner Mongolia, China [J]. Appl Soil Ecol,34 (2-3):266-275
Lotka AJ,1925. Elements of Physical Biology [M]. Williams and Wilkins, Baltimore
Manson C F.1979. Decomposition [M]. Studies in Biology,74. Edward Arnold
Meentemeyer V,1978. Macroclimate and lignin control of litter decomposition rates [J]. Ecology,59:465-472
Meissner R A, Facelli J M,1999. Effects of sheep exclusion on the soil seed bank and annual vegetation in chenopods shrub lands of South Australia [J]. J. Arid Environ,42:117-128
Merila P, Strammer R, Fritze H,2002. Soil microbial activity and community structure along a primary succession transect on the land-up lift coast in western Finland [J]. Soil Biology & Biochemistry, 34:1647-1654
Michaels AF,2003. The ratios of life [J]. Science,300:906-907
Mooney HA, Canadell J, Chapin Ⅲ FS, et al.,1999. Ecosystem physiology responses to global change. In: Walker B, Steffen W, Canadell J, and Ingram J, eds. The Terrestrial Biosphere and Global Change implications for natural and managed ecosystems [M], Cambridge Press,1999,41-189
Moretto AS, Distel RA, DidoneN G,2001. Decomposition and nutrient dynamic of leaf litter and roots from palatable and unpalatable grasses in a semi-arid grassland [J].Appl SoilEcol,18:31-37
Olsen, SR., Cole, CV., Watanabe, FS, and Dean, LA.,1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate [M]. U.S. Department of Agriculture Circular,939
Ottmun MJ, Tickes BR, Roth RL,1996. Alfalfa yield and stand response to termination in an arid environment [J]. Agronomy Journal,88:44-48
Puget P, Drinkwater LE,2001. Short term dynamics of root-and shoot-derived carbon from a leguminous green manure [J]. Soil Sci Soc Am J,65:771-779
Redfield AC,1958. The biological control of chemical factors in the environment [J]. American Scientist, 46:205-211
Reiners WA,1986. Complementary models for ecosystems [J]. American Naturalist,127:59-73
Reiz C, Maulder P, Begemann L,1988. Water Harvesting for Plant Production. World Bank, Washington.
Schindler D W,2003. Balancing planets and molecules [J]. Nature,423:225-226
Seastedt TR,1988. Mass, nitrogen, and phosphorus dynamics in foliage and root detritus of tall grass prairie [J]. Ecology,69(1):59-65
Seastedt TR, Parton WJ, Ojima DS,1992. Mass loss and nitrogen dynamics of decaying litter of grasslands: the apparent low nitrogen immobilization potential of root detritus [J]. Can JBot,70:384-391
Shan L, Liu ZM, Xin YQ, et al.1992. A study on the grass and field crops rotation in Mountain region of Southern Ningxia. The production and benefit of different rotation system [J]. Soil Water Cons,6 (4):60-68
Sherman F, Kuselman I,999. Stoichiometry and chemical metrology:Karl Fisher reaction [J]. Accreditation and Quality Assurance,4:230-234
Silver WL, Miya RK,2001. Global patterns in root decomposition:comparisons of climate and litter quality effects [J].Oecologia,129:407-419
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Taylor BR, Parkinson D, Parsons WF J,1989. Nitrogen and lignin content as predictors of litter decay rates:a microcosm test [J]. Ecology,70:97-104
Tessier JT, Raynal DJ,2003. Use of nitrogen to phosphorus ratios in plant tissue as an indicator of nutrient limitation and nitrogen saturation [J]. Journal of Applied Ecology,40:523-534
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Aerts R, DeCaluwe H,1999. Nitrogen deposition effects on carbon dioxide and methane emissions from temperate peat land soils [J].Oikos,84:44-54
Anderson JPE, Domsch KH,1980. Quantities of plant nutrients in the microbial biomass of selected soil [J]. Soil Sci,30:211-216
Bauder JW, Bauder A, Ramirez JM, Cassel DK,1987. Alfalfa water use and production on dry land and irrigated sandy loam [J]. Agronomy Journal,70:95-99
Blad BL, Rosenberg NJ,1976. Evaluation of resistance and mass transport evapotmnspiration models requiring canopy temperature data [J]. Agronomy Journd,68:764-769
Campbell CA, Biederbeck VO, Zenter RP, et al.,1991. Effect of crop rotation and cultural practices on soil organic matter, microbial biomass and respiration in a thin black chernozem [J]. Can J Soil Sci, 71:363-376
Chapin SF Ⅲ, Matson P, Mooney HA.2002. Principles of terrestrial ecosystem ecology [M]. Springer-Verlag, New York, Inc
Chen H, Harmon ME, Griffiths PR, et al.,2001. Effects of temperature and moisture on C respired from decomposing woody roots [J]. Forest Ecology and Management,138:51-64
Cotrufo MF, Inescon P,1996. Elevated CO2 reduces field decomposition rates of Betula pendula Roth. Leaf litter [J]. Oecologia,106:525-530
Disc NB, Matzner E, Forsius M,1998. Evaluation of organic horizon C:N ratio as an indicator of nitrate leaching in conifer forests across Europe [J]. Environmental Pollution,102(S1):453-456
Elser JJ, Dobberfuhl D, MacKay NA, Schampel J H,1996. Organism size, life history, and N:P stoichiometry:Towards a unified view of cellular and ecosystem processes [J]. BioScience,46:674-684
Elser JJ, Sterner RW, Gorokhova E, Fagan WF, Markow TA, Cotner JB, Harrison J F, Hobbie SE, Odell GM, Weider LW,2000b. Biological stoichiometry from genes to ecosystems [J]. Ecology Letters,3:540-550
Enriquez S, Duarte CM, Jensen, K,1993. Patterns in decomposition rates among photosynthetic organisms: the importance of detritus C:N:P content [J], Oecologia,94:457-471
Gathumbi SM, Bohlen PJ, Graetz DA,2005. Nutrient Enrichment of Wetland Vegetation and Sediments in Subtropical Pastures [J]. Soil Sci. Soc. Am. J.69:539-548
Gijsman AJ, Alarcon HF, Thomas RJ,1997. Root decomposition in tropical grasses and legumes as affected by soil texture and season. Soil Biol Biochem,29:1443-1450
Gundersen P, Callesen I, de Vries W.1998. Nitrate leaching in forest ecosystems is controlled by forest floor C/N ratio [J]. Environmental Pollution,102:403-407
Hessen DO,1997. Stoichiometry in food webs-Lotka revisited [J].Oikos,79,195-200
Hobbie SE,1996. Temperature and plant species control over litter decomposition in Alaskan tundra [J]. Ecol Monog,66:503-522
Jia Yu, Li FM, Wang XL, Xu JZ,2006. Dynamics of soil organic carbon and soil fertility affected by alfalfa productivity in a semiarid agro-ecosystem [J]. Biogeochemistry,80:233-243
Jiang HM, Jiang JP, Jia Y, Li FM, Xu JZ.2006. Soil carbon pool and effects of soil fertility in seeded alfalfa fields on the semi-arid Loess Plateau in China [J]. Soil Biology & Biochemistry,38:2350-2358
Kemp P R, Deborah GW, Clenton EO, James FR, Ross AV,1994. Effects of elevated CO2 and nitrogen fertilization pretreatments on decomposition on tallgrass prairie leaf litter [J]. Plant Soil,165:115-127
Koukoura Z,1998. Decomposition and nutrient release from C3 and C4 plant litters in a natural grassland [J]. Acta Oecol,19(2):115-123
Krogman KK, Hobbs EH,1965. Evapotranspiration of irrigated alfalfa as related to season and growth stage [J]. Canadian, Journal of Plant Science,45:310-313
Li FM, Song QH, Jjemba PK, Shi YC,2004. Dynamics of soil microbial biomass C and soil fertility in cropland mulched with plastic film in a semiarid agro-ecosystem [J]. Soil Biology & Biochemistry. 36:1893-1902
Li FM, Wang TC, Cao J,1998. Effect of organic matter on total amount and availability of nitrogen and phosphorus in Loess soil of Northwest China [J]. Communications in Soil Science and Plant Analysis. 29:947-953
Li FM, Xu JZ, Sun GJ,2003.Restoration of degraded ecosystems and development of water harvesting ecological agriculture in the semiarid Loess Plateau of China [J]. Acta Ecol Sin,23 (9):1901-1909
Lisa CW, Sebastien PCR, Ribriowx, et al.,2001. Phosphate availability regulates root system architecture in Arabidopsis [J]. Plant Physiol,126:875-882
Liu P, Huang JH, Han XG, Sun OJ, Zhou ZhY,2006. Differential responses of litter decomposition to increased soil nutrients and water between two contrasting grassland plant species of Inner Mongolia, China [J]. Appl Soil Ecol,34 (2-3):266-275
Lotka AJ,1925. Elements of Physical Biology [M]. Williams and Wilkins, Baltimore
Manson C F.1979. Decomposition [M]. Studies in Biology,74. Edward Arnold
Meentemeyer V,1978. Macroclimate and lignin control of litter decomposition rates [J]. Ecology,59:465-472
Meissner R A, Facelli J M,1999. Effects of sheep exclusion on the soil seed bank and annual vegetation in chenopods shrub lands of South Australia [J]. J. Arid Environ,42:117-128
Merila P, Strammer R, Fritze H,2002. Soil microbial activity and community structure along a primary succession transect on the land-up lift coast in western Finland [J]. Soil Biology & Biochemistry, 34:1647-1654
Michaels AF,2003. The ratios of life [J]. Science,300:906-907
Mooney HA, Canadell J, Chapin Ⅲ FS, et al.,1999. Ecosystem physiology responses to global change. In: Walker B, Steffen W, Canadell J, and Ingram J, eds. The Terrestrial Biosphere and Global Change implications for natural and managed ecosystems [M], Cambridge Press,1999,41-189
Moretto AS, Distel RA, DidoneN G,2001. Decomposition and nutrient dynamic of leaf litter and roots from palatable and unpalatable grasses in a semi-arid grassland [J].Appl SoilEcol,18:31-37
Olsen, SR., Cole, CV., Watanabe, FS, and Dean, LA.,1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate [M]. U.S. Department of Agriculture Circular,939
Ottmun MJ, Tickes BR, Roth RL,1996. Alfalfa yield and stand response to termination in an arid environment [J]. Agronomy Journal,88:44-48
Puget P, Drinkwater LE,2001. Short term dynamics of root-and shoot-derived carbon from a leguminous green manure [J]. Soil Sci Soc Am J,65:771-779
Redfield AC,1958. The biological control of chemical factors in the environment [J]. American Scientist, 46:205-211
Reiners WA,1986. Complementary models for ecosystems [J]. American Naturalist,127:59-73
Reiz C, Maulder P, Begemann L,1988. Water Harvesting for Plant Production. World Bank, Washington.
Schindler D W,2003. Balancing planets and molecules [J]. Nature,423:225-226
Seastedt TR,1988. Mass, nitrogen, and phosphorus dynamics in foliage and root detritus of tall grass prairie [J]. Ecology,69(1):59-65
Seastedt TR, Parton WJ, Ojima DS,1992. Mass loss and nitrogen dynamics of decaying litter of grasslands: the apparent low nitrogen immobilization potential of root detritus [J]. Can JBot,70:384-391
Shan L, Liu ZM, Xin YQ, et al.1992. A study on the grass and field crops rotation in Mountain region of Southern Ningxia. The production and benefit of different rotation system [J]. Soil Water Cons,6 (4):60-68
Sherman F, Kuselman I,999. Stoichiometry and chemical metrology:Karl Fisher reaction [J]. Accreditation and Quality Assurance,4:230-234
Silver WL, Miya RK,2001. Global patterns in root decomposition:comparisons of climate and litter quality effects [J].Oecologia,129:407-419
Strian CL, R andall DC, Turner FB,1987. Relationship of leaf decomposition rate to rainfall in the Mojave Desert [J]. Ecology,68 (3):741-744
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