Productivity of well-watered Panicum virgatum does not increase with CO2 enrichment
Productivity of well-watered Panicum virgatum does not increase with CO2 enrichment
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DOI：
10.1093/jpe/rts007
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发表时间：
2012-10-01
影响因子：
2.7
通讯作者：
Aspinwall, Michael J.
中科院分区：
文献类型：
--
作者：
Fay, Philip A.;Polley, H. Wayne;Aspinwall, Michael J.
在缺水的多年生草原上，大气中二氧化碳浓度的增加被证明能够提高地上净初级生产力，部分原因是减少了气孔导度和蒸腾作用，从而减少了土壤水分的消耗。然而，土壤类型不同，二氧化碳浓度升高对ANPP的益处也不同，如果水分限制较低，则可能会减少。关于CO2对多年生C-4高粱和潜在的生物能源作物黑麦草ANPP的影响，人们知之甚少。我们假设，如果水分限制最小，(I)增施CO2不会增加黄花草的ANPP，因为这种C-4草的光合作用不会增加，而且高CO2下蒸腾作用的减少在增加土壤水分方面几乎没有额外的好处，(Ii)土壤类型对黄花草的CO2响应几乎没有影响，因为土壤总体水分较高。‘Alamo’是在美国得克萨斯州中部的粉质粘土和粘性土壤上沿L L(-1)大气CO2梯度种植了4年的植物。植株浇水以代替蒸散，施以硝酸铵和五氧化二磷，并在季节中期修剪到标准高度。在生长的第三年，净初级生产力增加。土壤水分(0-20 cm)、ANPP、分蘖数和叶面积指数在粘性土上比粉质粘性土高8-18%。除种植年份外，土壤净现值均不随CO2浓度的增加而增加。然而，在第2年和第3年，剪枝去除的生物量随着CO2的增加而显著增加，这表明CO2的增加增加了初生草和成熟植株的早期到中期的生长，但不能促进后期的再生或完全建成的植株的生长。此外，CO2浓度升高在第2年和第3年对ANPP的两个组成部分产生了不同的影响，增加了分蘖质量，减少了分蘖数量。这种资源的重新分配表明，随着CO2浓度的增加，分生组织对生产力的限制增加。CO2浓度的增加对光合作用的影响不大，但随着植株的建立，气孔导度和蒸腾作用逐渐降低。结果表明，随着植株叶面积的增加，水分利用效率与CO2的耦合程度越来越大。这些结果表明，对于充分浇水和修剪的青杨来说，ANPP因土壤类型的不同而不同，在完全建立时不受CO2增加的影响，但在建立过程中与修剪相互作用改变了分配模式。当水分更受限制时，土壤类型对ANPP-CO2响应的影响可能会变得更加明显。
Rising atmospheric CO2 has been shown to increase aboveground net primary productivity (ANPP) in water-limited perennial grasslands, in part by reducing stomatal conductance and transpiration, thereby reducing depletion of soil moisture. However, the benefits of CO2 enrichment for ANPP will vary with soil type and may be reduced if water limitation is low. Little is known about CO2 effects on ANPP of Panicum virgatum, a perennial C-4 tallgrass and potential bioenergy crop. We hypothesized that if water limitation is minimized, (i) CO2 enrichment would not increase P. virgatum ANPP because photosynthetic rates of this C-4 grass would not increase and because decreased transpiration at elevated CO2 would provide little additional benefit in increased soil moisture and (ii) soil type will have little effect on P. virgatum CO2 responses because of high overall soil moisture.Growth and leaf physiology of P. virgatum cv. 'Alamo' were studied as plants established for 4 years on silty clay and clay soils along a 250 to 500 mu l l(-1) gradient in atmospheric CO2 located in central Texas, USA. Plants were watered to replace evapotranspiration, fertilized with NO3NH4 and P2O5 and clipped to standard height during mid-season.ANPP increased through the third year of growth. Soil moisture (0-20 cm), ANPP, tiller numbers and leaf area index were 8-18% higher on the clay than on the silty clay soil. ANPP did not increase with CO2 except in the planting year. However, biomass removed with clipping strongly increased with CO2 in years 2 and 3, suggesting that CO2 enrichment increased the early- to mid-season growth of establishing P. virgatum but not later regrowth or that of fully established plants. Furthermore, CO2 enrichment differentially affected two components of ANPP in years 2 and 3, increasing tiller mass and reducing tiller numbers. This reallocation of resources in clipped P. virgatum suggested increased meristem limitation of productivity with CO2 enrichment. CO2 enrichment had little effect on photosynthesis but increasingly reduced stomatal conductance and transpiration as the plants established. As a result, water use efficiency became increasingly coupled to CO2 as leaf area increased during establishment. These results suggest that for well-watered and clipped P. virgatum, ANPP differed between soil types, was not affected by CO2 enrichment when fully established but interacted with clipping to alter allocation patterns during establishment. Soil type effects on ANPP-CO2 responses will likely become more apparent when water is more limiting.