干旱区生态环境知识资源中心

The higher water to dry matter conversion efficiency of CAM plants than C3 and C4 plants can permit higher productivity per mm of rainfall than these other photosynthetic systems. However in arid regions, low annual N inputs of about 2 kg/ha from all non symbiotic sources combined (rainfall, blue-green algal crusts etc) place a low ceiling on the sustainable productivity. This paper compares the productivity possible with published transpiration coefficients of C3, C4 and CAM plants, with protein levels typical of legumes 24%, grasses 10% and un fertilized cactus (5%) and at natural inputs of 2 kg ha(-1) yr(-1) and with modest N fertilization of 40 kg N ha(-1) yr(-1). The paper also compares the high Ca and K contents of cactus pear fruits and stems (cladodes) to other perennial fruit plants, with regard to the influence of these minerals on fruit productivity.