Asymmetry in above‐ and belowground productivity responses to N addition in a semi‐arid temperate steppe
Asymmetry in above‐ and belowground productivity responses to N addition in a semi‐arid temperate steppe
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DOI：
10.1111/gcb.14719
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发表时间：
2019-06
影响因子：
11.6
通讯作者：
Jing Wang;Yingzhi Gao;Yunhai Zhang;Junjie Yang;Melinda D. Smith;A. Knapp;D. Eissenstat;Xingguo Han
中科院分区：
文献类型：
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作者：
Jing Wang;Yingzhi Gao;Yunhai Zhang;Junjie Yang;Melinda D. Smith;A. Knapp;D. Eissenstat;Xingguo Han
氮(N)的增加通常会增加生态系统的地上净初级生产力(ANPP)，但地下净初级生产力(BNPP)是否跟踪ANPP的响应尚不清楚。此外，N投入的频率可能会影响初级生产力，但很少有人研究。为了评价不同施氮频率下地上和地下生产力对施氮量的响应模式，我们在中国北部温带草地连续6年控制了NH4NO3的施用量(0-50g N m−2年−1)和频率(每年2次与每月1次施氮)，并于2012年至2014年进行了净初级生产力和净初级生产力的测定。在低施氮量范围内，随着施氮量(<；10g N m−2年−1)的增加，氮肥对氮肥的负效应最大，对氮素的正效应最大。当N添加超过10g N m−2a−1时，ANPP的增加受到抑制，而BNPP的下降完全停止。净第一性生产力(地上和地下结合；NPP)的响应模式与ANPP的对应关系比与BNPP的对应关系更密切。在与氮素沉积相关的氮素添加范围内，氮素对BNPP和BNPP/NPP(FBNPP)的影响不依赖于氮素添加频率。BNPP比ANPP对氮素添加频率更敏感，尤其是在低氮素添加速率下。我们的发现为植物如何通过增加氮素水平和改变添加频率来调节不同器官的碳分配提供了新的见解。如果将这些根响应模式纳入地球系统模型，可能会提高面对全球大气氮沉积时旱地生态系统中碳动态的预测能力。
Nitrogen (N) enrichment often increases aboveground net primary productivity (ANPP) of the ecosystem, but it is unclear if belowground net primary productivity (BNPP) track responses of ANPP. Moreover, the frequency of N inputs may affect primary productivity but is rarely studied. To assess the response patterns of above‐ and belowground productivity to rates of N addition under different addition frequencies, we manipulated the rate (0–50 g N m−2 year−1) and frequency (twice vs. monthly additions per year) of NH4NO3 inputs for six consecutive years in a temperate grassland in northern China and measured ANPP and BNPP from 2012 to 2014. In the low range of N addition rates, BNPP showed the greatest negative response and ANPP showed the greatest positive responses with increases in N addition (<10 g N m−2 year−1). As N addition increased beyond 10 g N m−2 year−1, increases in ANPP dampened and decreases in BNPP ceased altogether. The response pattern of net primary productivity (combined above‐ and belowground; NPP) corresponded more closely to ANPP than to BNPP. The N effects on BNPP and BNPP/NPP (fBNPP) were not dependent on N addition frequency in the range of N additions typically associated with N deposition. BNPP was more sensitive to N addition frequency than ANPP, especially at low rates of N addition. Our findings provide new insights into how plants regulate carbon allocation to different organs with increasing N rates and changing addition frequencies. These root response patterns, if incorporated into Earth system models, may improve the predictive power of C dynamics in dryland ecosystems in the face of global atmospheric N deposition.