青藏高原两种植被类型净初级生产力与气候因素的关系及周转值分析

基于2008—2016年青海海北站9年净初级生产力及气候因子监测数据,分析了青藏高原高寒小嵩草草甸和高寒金露梅灌丛两种植被净初级生产力年际动态,并探讨了气候因子对其影响及其不同土层深度根系周转值特征。结果表明:(1)年际尺度上,小嵩草草甸地上净初级生产力表现为显著增加趋势,增幅为7.02 g m~(-2) a~(-1),而金露梅灌丛地上净初级生产力相对较为稳定;对于其地下净初级生产力和总生产力,小嵩草草甸和金露梅灌丛均表现为增加趋势(P0.05),9年间小嵩草草甸地上、地下和总净初级生产力平均值分别为(217.55±9.95)、(1882.75±161.33) g m~(-2) a~(-1)和(2100.30±163.38) g m~(-2) a~(-1),金露梅灌丛地上、地下和总净初级生产力9年间平均值分别为(256.27±11.4)、(1614.31±173.03) g m~(-2) a~(-1)和(1870.58±177.93) g m~(-2) a~(-1)。(2)不同植被类型地上净初级生产力对气候因素响应不同,金露梅灌丛地上净初级生产力主要受温度影响,而温度对小嵩草草甸地上净初级生产力无显著影响。此外,降水不是限制高寒生态系统草地地上净初级生产力主要因子,相比于降水影响,高寒生态系统地上净初级生产力更受温度调控。(3)年均温和年降水对金露梅灌丛和小嵩草草甸地下净初级生产力均无显著影响(P0.05),表明高寒生态系统,其地下生产力受外界气候条件变化影响微弱,是一个稳定的碳库。(4)两种植被类型其根系周转值均随着土壤深度的增加呈逐渐增加趋势,且高寒灌丛根系周转值明显高于高寒草甸根系周转值。研究表明,在全球气候变暖背景下将会增加金露梅灌丛地上净初级生产力,而对小嵩草草甸地上净初级生产力无显著影响。

The response of net primary productivity of two different vegetation types to climatic factors and root turnover analysis on the Qinghai-Tibet Plateau

Based on nine years (from 2008 to 2016) of monitoring data of net primary productivity (NPP) and climatic factors at Haibei Station, the interannual NPP dynamics of alpine Kobresia pygmaea meadow and alpine Potentilla fruticosa shrubs were analyzed. In addition, the effects of climatic factors on NPP and the characteristics of root turnover across different soil layers were also assessed. The results showed that (1) on an interannual scale, the aboveground net primary productivity (ANPP) of Kobresia pygmaea meadow showed a significant increasing trend (7.02 g m^-2 a^-1), but the ANPP of Potentilla fruticosa shrubs remained relatively stable. Both belowground net primary productivity (BNPP) and total net primary productivity (NPP) of the two vegetation types showed a slight increase (P>0.05). The average ANPP, BNPP, and NPP for the Kobresia pygmaea meadow were (217.55±9.95) g/m², (1882.75±161.33) g/m² and (2100.30±163.38) g/m², respectively. The average ANPP, BNPP, and NPP for Potentilla fruticosa shrubs were (256.27 ±11.4) g/m², (1614.31 ±173.03) g/m², and (1870.58±177.93) g/m², respectively. (2) The ANPP of the vegetation types responded differently to climatic factors. The mean annual air temperature had a significant effect on ANPP for Potentilla fruticosa shrubs, but no significant impact on the ANPP of Kobresia pygmaea meadow. Furthermore, precipitation was not a key factor limiting the NPP of grassland in alpine ecosystems; temperature exerted a stronger effect on the ANPP of alpine ecosystems compared with precipitation. (3) The mean annual air temperature and mean annual precipitation showed no notable effect on the BNPP, indicating that the BNPP was less affected by external climatic factors than the ANPP. (4) Root turnover increased with soil depth and the root turnover of Potentilla fruticosa shrubs was higher than that of Kobresia pygmaea meadow. Our study implies that the ANPP of Potentilla fruticosa shrubs will increase with climate change, but no significant change is expected for the ANPP of Kobresia pygmaea meadow.