Nitrogen limitation in dryland ecosystems: Responses to geographical and temporal variation in precipitation
Nitrogen limitation in dryland ecosystems: Responses to geographical and temporal variation in precipitation
复制标题
DOI：
10.1007/bf01007582
复制
发表时间：
1999-07-01
期刊：
影响因子：
4
通讯作者：
Johnson, L
中科院分区：
文献类型：
--
作者：
Hooper, DU;Johnson, L
研究了旱地生态系统植物氮素限制与水分有效性的关系。在年降水量较低的条件下，地面净初级生产力（ANPP）主要受水分的限制，而在年降水量较高的条件下，其主要受氮的限制。通过对干旱、半干旱和半湿润生态系统施肥试验的文献综述，研究了ANPP对氮添加的响应随不同地理梯度降水的变化，以及站点内降水的年际变化。采用4个指标评价氮素限制程度：(1)不同年降水量下植物产量对施肥响应的绝对增长量（ANPP斜率vs. N添加量）；(2)相对响应（不同施氮水平下施氮量较对照增加的百分比）；(3)肥料利用效率（FUE，单位氮肥产量的绝对增益）和(4)最大响应（氮添加饱和水平下ANPP的最大绝对增加）。无论在地理梯度上还是在立地内的年际变化上，施肥的相对响应都不随降水量的增加而显著增加。在不同的地理梯度上，施肥的最大响应也没有随着降水的增加而增加。另一方面，降水的绝对增长量和FUE指数在地理和时间上都有显著的增加。综上所述，这些结果表明，在整个地理水有效性梯度上，主要限制并不一定是从水向氮转移。相反，我们的结果支持共同限制的假设。氮限制4个指标的结果明显相互矛盾，这可以用植物生态生理、群落和生态系统机制的整合来解释，即植物受到多种资源的共同限制，物种迁移是对资源水平变化的响应，氮和水的有效性通过生物地球化学反馈紧密联系在一起。
We investigated the relationship between plant nitrogen limitation and water availability in dryland ecosystems. We tested the hypothesis that at lower levels of annual precipitation, aboveground net primary productivity (ANPP) is limited primarily by water whereas at higher levels of precipitation, it is limited primarily by nitrogen. Using a literature survey of fertilization experiments in arid, semi-arid, and subhumid ecosystems, we investigated the response of ANPP to nitrogen addition as a function of variation in precipitation across geographic gradients, as well as across year-to-year variation in precipitation within sites. We used four different indices to assess the degree of N limitation: (1) Absolute Increase of plant production in response to fertilization (the slope of ANPP vs. amount of added N at different levels of annual precipitation); (2) Relative Response (the percent increase in fertilized over control ANPP at different levels of N addition); (3) Fertilizer Use Efficiency (FUE, the absolute gain in productivity per amount of fertilizer N), and (4) Maximum Response (the greatest absolute increase in ANPP at saturating levels of N addition). Relative Response to fertilization did not significantly increase with increasing precipitation either across the geographic gradient or across year-to-year variation within sites. Nor did the Maximum Response to fertilization increase with increasing precipitation across the geographic gradient. On the other hand, there was a significant increase in the Absolute Increase and FUE indices with both geographical and temporal variation in precipitation. Together, these results indicate that there is not necessarily a shift of primary limitation from water to N across the geographic water availability gradient. Instead, our results support the hypothesis of co-limitation. The apparently contradictory results from the four indices of N limitation can best be explained by an integration of plant ecophysiological, community, and ecosystem mechanisms whereby plants are co-limited by multiple resources, species shifts occur in response to changing resource levels, and nitrogen and water availability are tightly linked through biogeochemical feedbacks.