碳氮添加对草地土壤有机碳氮磷含量及相关酶活性的影响

Effects of carbon and nitrogen additions on soil organic C,N,P contents and their catalyzed enzyme activities in a grassland

草地土壤有机碳(C)、氮(N)、磷(P)等养分含量和酶活性对草地生态系统能量和养分的保持和供应具有重要作用.氮沉降对草地生态系统土壤有机养分及酶活性产生影响的结果不一致性,碳的同步添加是否会缓解氮沉降造成的负面影响仍不清楚,需要深入探讨.本研究以在内蒙古呼伦贝尔草原开展的碳(葡萄糖)、氮(尿素)添加试验样地为依托(始于2014年5月),探讨碳、氮添加对草地土壤C、N、P含量及相关酶活性的影响及其机制.试验分别设N0(对照)、N_(25)(施氮25 kg·hm^(-2)·a^(-1))、N_(50)(50 kg·hm^(-2)·a^(-1))、N100(100 kg·hm^(-2)·a^(-1))、N_(200)(200 kg·hm^(-2)·a^(-1))共5个N添加主处理,C_0(对照)、C_(250)(施碳250 kg·hm^(-2)·a^(-1))、C500(500 kg·hm^(-2)·a^(-1))3个碳添加副处理,试验样品采于2016年8月.结果表明:高氮添加显著抑制脱氢酶(DHA)和β^(-1),4-N-乙酰氨基葡糖苷酶(NAG)活性,与对照相比,其活性分别降低22.3%和12.5%;而氮添加对土壤有机N含量无显著影响,使有机C和有机P含量分别减少6.6%和14.5%.高碳添加缓解了土壤微生物的碳限制,使得脱氢酶(DHA)、β-葡糖苷酶(BG)活性及土壤有机N、有机P含量分别增加15.1%、12.2%、1.9%、2.6%.研究表明,长期过量氮输入抑制土壤微生物活性,造成土壤有机C、有机P的减少,而碳添加提高了微生物及酶活性,使土壤有机N、P含量增加.碳氮耦合添加对草地土壤有机C、N、P的持续供应具有重要意义.

Soil organic C,N,P contents and their catalyzed enzyme activities play an important role in maintaining and supplying energy and nutrient in grasslands. There is no consensus on the effects of N deposition on soil organic nutrients and enzyme activities in grassland ecosystems. It remains unclear whether C addition will retard the negative effects of N deposition. We carried out an experiment in Hulun Buir grassland of Inner Mongolia to examine the effects of C and N additions on soil organic C,N,P and relative enzyme activities after three years treatments. The experiment was conducted with N treatments at five levels（ 0,25,50,100 and 200 kg·hm-2·a-1） and with C treatments at three levels（ 0,250 and 500 kg · hm-2·a-1）. The results showed that higher levels of N addition significantly decreased dehydrogenase（ DHA） and β-1,4-N-acetylglucosaminidase（ NAG） activities by 22. 3% and 12. 5%,respectively. Nitrogen addition had no significant effect on soil organic N and decreased the organic C and P contents by 6.6% and 14.5%,respectively.High C addition significantly increased DHA,β-glucosidase（ BG） activities and increased soil organic N and organic P by 15.1%,12.2%,1.9%,2.6%,respectively. The results suggested that continuous N inputs inhibited microbial activities and caused losses of soil organic C and organic P. Carbon addition could enhance microbial activities and promote the secretion of enzymes and increase soil organic N and P. The combined C and N addition could play an important role in maintaining the balance and supply of soil C,N,and P in grassland ecosystem.