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Revegetation has significantly contributed to improvements in ecosystem services, such as carbon sequestration and soil retention. Yet, vegetation expansion in water-limited regions may generate conflict of water demand between nature and humans. Present studies are still lacking when it comes to identifying the permissible vegetation capacity, i.e. net primary productivity (NPP) threshold, based on the local water resources limits, and further proposing adjustment and optimization strategies to keep water use balanced in anthropogenic-biological systems. Under such a circumstance, this study assesses the difference between the actual NPP and NPP thresholds at regional and ecosystem scales in China. The results show that 8 out of 31 provinces have their provincial actual NPP above the regional NPP thresholds, mainly concentrated in northern China between 400 and 800 mm iso-precipitation line, i.e. North China Plain (Beijing-Tianjin-Hebei), the middle reaches of the Yellow River Basin (Shaanxi and Henan provinces), and the Northeast China (Heilongjiang, Jilin and Liaoning). Forest ecosystems dominate the difference between the actual total woodland and grassland ecosystems NPP and the permissible NPP thresholds in these regions, ranging from 67% (Beijing) to 99% (Tianjin). If the current vegetation intensity in these regions remains unchanged, the areas of woodland and grassland ecosystems should be optimized 0–48% and 0–100% of their present areas to balance the water demand between the ecosystems and humans, without considering the potential consequence of climate change and soil erosion. Although 23 provinces have their regional actual NPP below their permissible NPP thresholds, 6 out of 23 provinces still have their woodland and grassland ecosystems NPP above the corresponding NPP thresholds, mainly focusing on the Northwestern China north over the 400 mm iso-precipitation line, including Inner Mongolia, Qinghai, Hainan, Shanxi, Gansu and Xinjiang. Forest ecosystems also dominate the negative NPP differences in these regions, ranging from 91% (Inner Mongolia) to 46% (Gansu). These reveal the hidden and potential pressure in the 6 provinces to balance limited water resources in the local anthropogenic-biological system. This study provides a method to assess the water-resources permissible NPP threshold and further proposes the specific adjustment and optimization plans for the areas with actual NPP above the corresponding NPP thresholds, which can provide guidance for ecological restoration program implementations in a more sustainable way.

重建植被極大地促進了生態(tài)系統(tǒng)服務的改善，如碳固存和土壤保持。然而，在水資源有限的地區(qū)，植被的擴張可能會產(chǎn)生自然與人類之間的用水需求沖突。目前的研究仍然缺乏在當?shù)厮Y源限制的基礎上確定允許的植被容量，即凈初級生產(chǎn)力(NPP)閾值，并進一步提出調整和優(yōu)化策略以保持人類-生物系統(tǒng)中的用水平衡。在這種情況下，本研究評估了中國區(qū)域和生態(tài)系統(tǒng)尺度上的實際NPP和NPP閾值之間的差異。結果表明，31個省份中有8個省份的實際NPP高于區(qū)域NPP閾值，主要集中在華北平原(京津冀)、黃河中游(陜西、河南)和東北地區(qū)(黑龍江、吉林、遼寧)。在這些地區(qū)，森林生態(tài)系統(tǒng)在林地和草地生態(tài)系統(tǒng)實際總NPP和允許NPP閾值之間的差異中占主導地位，范圍從67%(北京)到99%(天津)。如果這些地區(qū)目前的植被密度保持不變，林地和草地生態(tài)系統(tǒng)的面積應該優(yōu)化為目前面積的0-48%和0-100 %,以平衡生態(tài)系統(tǒng)和人類之間的需水量，而不考慮氣候變化和土壤侵蝕的潛在后果。盡管23個省份的區(qū)域實際NPP低于其允許NPP閾值，但其中6個省份的林地和草地生態(tài)系統(tǒng)NPP仍高于相應的NPP閾值，主要集中在400 mm等雨量線以上的中國西北地區(qū)，包括內蒙古、青海、海南、山西、甘肅和新疆。森林生態(tài)系統(tǒng)也在這些地區(qū)的負NPP差異中占主導地位，范圍從91%(內蒙古)到46%(甘肅)。這揭示了這6個省在平衡當?shù)厝祟?生物系統(tǒng)中有限的水資源方面隱藏的和潛在的壓力。本研究提供了一種評估水資源允許凈第一性生產(chǎn)力閾值的方法，并對實際凈第一性生產(chǎn)力高于相應的凈第一性生產(chǎn)力閾值的地區(qū)提出了具體的調整和優(yōu)化方案，為生態(tài)修復工程的可持續(xù)實施提供了指導。