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Title: Response of soil-microbe-extracellular enzyme stoichiometric characteristics to nitrogen deposition in a Pinus yunnanensis forest in central Yunnan Province, Southwest China.
Author: Wang Q, Wang KQ, Song YL, Chen YQ, Peng XY, Deng QJ.
Journal: Ying Yong Sheng Tai Xue Bao; 2024 Jul 18; 35(7):1789-1798. PubMed ID: 39233407.
Abstract:
To understand the effects of nitrogen deposition on element cycling and nutrient limitation status in forest ecosystems, we examined the effects of nitrogen deposition on the stoichiometric characteristics of forest soil-microbial-extracellular enzymes in Pinus yunnanensis forest. We conducted a field experiment with control (CK, 0 g N·m^-2·a^-1), low nitrogen (LN, 10 g N·m^-2·a^-1), medium nitrogen (MN, 20 g N·m^-2·a^-1) and high nitrogen (HN, 25 g N·m^-2·a^-1) since 2019. We collected soil samples (0-5 cm, 5-10 cm and 10-20 cm) at September 2022, and measured the contents of soil organic, total nitrogen, total phosphorus, microbial biomass carbon, nitrogen and phosphorus (MBC, MBN, MBP) and the activities of C, N, and P acquisition enzymes. The results showed that nitrogen deposition significantly reduced soil organic content, C:N and C:P by 6.9%-29.8%, 7.6%-45.2% and 6.5%-28.6%, and increased soil total N content and N:P by 10.0%-45.0% and 19.0%-46.0%, respectively. Nitrogen addition did not affect soil total P content. Except for soil C:N and C:P, soil nutrient content and stoichiometric ratio were highest in 0-5 cm soil layer. MN and HN treatments significantly decreased MBN by 11.0%-12.7%. MBC, MBP, and their stoichiometry did not change significantly under nitrogen deposition. Soil microbial nutrient content in 0-5 cm soil layer was significantly higher than that in other soil layers. Nitrogen deposition significantly decreased the activities of cellobiose hydrolase and leucine aminopeptidase (decreased by 14.5%-16.2% and 48.7%-66.3%). HN treatment promoted β-1,4-glucosidase activity (increased by 68.0%), but inhibited soil enzyme stoichiometric carbon to nitrogen ratio and nitrogen to phosphorus ratio (decreased by 95.4% and 88.4%). LN and MN treatment promoted β-1,4-N-acetylglucosaminidase activity (increased by 68.3%-116.6%), but inhibited enzyme stoichiometric carbon to phosphorus ratio (decreased by 14.9%-29.4%). Alkaline phosphatase activity had no significant change. Soil enzyme activities were significantly decreased with increasing soil depth. Soil total N and total P and microbial nutrients were negatively correlated with vector angle (representing microbial nitrogen or phosphorus limitation), while vector length (representing microbial carbon limitation) was consistently significantly positively correlated with vector angle, suggesting the synergistic promotion between microbial carbon limitation and phosphorus limitation. Nitrogen deposition gradually shifted to phosphorus limitation while alleviating microbial nitrogen limitation in P. yunnanensis forest. In addition, microbial activities in this region was limited by C availability, and the relationship between microbial C and P limitation was proportional. 开展氮沉降对森林土壤-微生物-胞外酶化学计量特征影响的研究,可为理解氮沉降对森林生态系统元素循环和养分限制的影响提供理论基础。本研究以云南松林为对象,于2019年开始进行氮沉降模拟试验,设置对照(CK,0 g N·m^-2·a^-1)、低氮(LN,10 g N·m^-2·a^-1)、中氮(MN,20 g N·m^-2·a^-1)、高氮(HN,25 g N·m^-2·a^-1)4个处理,于2022年9月采集土壤样品(分为0～5、5～10、10～20 cm土层)测定土壤有机碳、全氮、全磷、微生物生物量碳氮磷(MBC、MBN、MBP)以及碳氮磷获取酶活性。结果表明: 与对照相比,氮沉降显著抑制了土壤有机碳含量、C∶N和C∶P,降幅分别为6.9%～29.8%、7.6%～45.2%和6.5%～28.6%;促进了土壤全氮含量和N∶P,增幅分别为10.0%～45.0%和19.0%～46.0%;对土壤全磷含量则无显著影响;除土壤C∶N和C∶P外,土壤养分含量及化学计量比均在0～5 cm土层最高。MN和HN处理显著抑制了土壤MBN,降幅为11.0%～12.7%,氮沉降下土壤MBC和MBP及相关计量比无显著变化;0～5 cm土层的土壤微生物养分含量显著高于其余土层。氮沉降显著抑制了纤维素二糖水解酶和亮氨酸氨基肽酶活性(降幅为14.5%～16.2%和48.7%～66.3%);HN处理促进了β-1,4-葡萄糖苷酶活性(增幅68.0%),但抑制了土壤酶化学计量碳氮比和氮磷比(降幅95.4%和88.4%);LN和MN处理促进了β-1,4-N-乙酰氨基葡萄糖苷酶活性(增幅68.3%～116.6%),但抑制了土壤酶化学计量碳磷比(降幅14.9%～29.4%);碱性磷酸酶活性无显著变化;土壤酶活性均随土层加深而显著降低。相关性分析表明,土壤全氮、全磷、微生物养分与矢量角度(表征微生物氮或磷限制)均呈显著负相关,而矢量长度(表征微生物碳限制)与矢量角度始终呈显著正相关,代表微生物碳限制与磷限制之间协同促进。氮沉降在缓解云南松林微生物氮限制的同时逐渐向磷限制转变,此外,研究区还受到微生物碳限制,且微生物碳和磷限制的关系呈正比。.

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