黄土高原丘陵沟壑区小流域植被净第一性生产力模型

A simulation model of net primary production at watershed scale in hilly area of Loess Plateau, China

构建了机理性植被净第一性生产力模型(Vegetation- Soil- Integrated- Model,VSIM) ,该模型将土壤水分动态过程与植被生长过程相耦合,用以分析黄土高原丘陵沟壑区土壤水分对植被生产力的影响。模型考虑了叶片尺度上气孔导度对净光合过程和蒸腾过程的影响,在此基础上通过考虑植被冠层结构和地形因素的影响对模型进行尺度转换,并以位于黄土高原丘陵沟壑区纸坊沟流域的观测数据对模型进行参数化和验证。结果表明对于生物量的模拟草本和半灌木比乔、灌木好,主要植被类型L AI的季节变化与观测结果具有很好的一致性,模型能够反映出流域降雨-产流过程,并且基本上也能够反映土壤水分的时空变化范围。模拟结果表明,刺槐林和苹果林属于高光合-低蒸腾类型,农作物、白羊草群落和达乌里胡枝子群落属于高光合-高蒸腾类型,铁杆蒿群落和茭蒿群落属于低光合-低蒸腾类型,而沙棘灌丛和柠条灌丛的净第一性生产力居中,但蒸腾量较高。流域内土壤水分在多年序列上基本平衡,而在不同的水文年表现出失衡。其中刺槐林、苹果林和沙棘灌丛的多年平均土壤水分在年内存在少量亏缺,铁杆蒿群落和茭蒿群落略有增加,而其它植被类型基本保持平衡。丰水年不同植被类型土壤含水量都明显高于欠水年,土壤水分含量的变化在丰水年表现为盈余,而在?

The hilly area of loess plateau is well known for its high erosion rate and sensitive to the global change for their vulnerable ecosystem. Vegetation is the main factor to improve the environment of soil erosion and water loss. The net primary production is the significant characteristic of ecosystem structure and function. The production of different vegetation types and plant species under various environmental conditions reflect their adaptability to Loess Plateau. In arid and semiarid ecosystem of Loess Plateau of China, the average soil moisture is quite low and the patterns of seasonal precipitation and the quantity of soil water availability are highly variable. Because of this, water is a major determination of ecosystem processes. Modeling soil water dynamic and soil moisture spatial distribution at watershed scale are very important. A model (VSIM) to simulate net primary production model at watershed scale was developed to explore the effect of soil water dynamic on the primary production processes. The model coupled a soil water dynamic module and a vegetation growth module. The former is a daily time step, multi-horizon, distributed spatial model. The later included a mechanism model of stomotal conductance based on the mechanical character of guard cell, which used to reflect both the influence of soil water potential to stomatal conductance and the stomotal control to net photosynthesis and transpiration processes at leaf scale. Scaling up to canopy and watershed scale through considered the effect of canopy structure and heterogeneity of topography. The main inputs of the model include photosynthetic characteristics of main vegetation type, meteorological data,soil texture and physical properties. The outputs are soil water of 4 soil layers, evaporation, transpiration, runoff, net primary production and biomass of leaf, stem and root. The model was used in Zhifanggou watershed, which located in forest steppe zone and belonged to hilly area of Loess Plateau, and the model validation was tested by observation data sets. In the modeling experiment, simulations show to provide good approximation with field observation data. The simulation of biomass of grass and sub-shrub are better than that of arbor and shrub, and the dynamic of LAI of main vegetation types have well coherence with the observation results. The model could reflect the processes of precipitation-runoff at the watershed, and could indicate the spatio- temporal changes of soil water content. The simulation results show that (1)Form. R. pseudoacaciat and M. pumila have highest primary production with lower transpiration, and crop, Form. B. ischaemum and L.davurica have higher primary production with highest transpiration, and the primary production and transpiration of Form. A. gmelinii and A. giradii. are all lowest, while Form. H. rhamnoides and C. korshinskii have moderate primary production with higher transpiration. (2) Soil water keep balance at long term, but with fluctuating in short term. Soil moisture of Form. R. pseudoacaciat, M. pumila and H. rhamnoides is deficit higher, soil water is complemented at end of year for Form. A. gmelini and A. giradii, and soil water keep balance for others. Soil moisture is higher in high-flow year than that in low-flow year for all vegetation types, and shows serious deficit in low-flow year and abundant in high-flow year.