将桑树和大豆分别单独种植(单作)或两种隔行种植(间作),测得两种植物的光合速率如图所示(注:光饱和点是光合速率达到最大值时所需的最低光照强度),据图分析,下列叙述正确的是( )。
- A.与单作相比,间作时两种植物的呼吸强度均没有受到影响
- B.与单作相比,间作时两种植物光合作用的光饱和点均增大
- C.间作虽然提高了桑树的光合速率但降低了大豆的光合速率
- D.大豆植株开始积累有机物时的最低光照强度单作大于间作
正确答案及解析
正确答案
解析
图中桑树和大豆间作时的光合速率与单作时的光合速率不是一致的,说明间作对于植物来讲是有影响的,曲线显示桑树间作时呼吸作用变大,大豆间作时呼吸作用变小,故A选项错误;图中显示与间作相比,桑树间作时光合作用的光饱和点增大,而大豆减小,故B选项错误;大豆在光照强度达到两条曲线相交之前(如5)时,间作的光合速率是比单作还要高的,故C选项错误;曲线与横坐标的交点(即光补偿点)代表光合作用与呼吸作用相等,此点之后植物开始积累有机物,右图显示大豆单作光补偿点大于间作,所以大豆植株开始积累有机物时的最低光照强度单作大于间作,故D选项正确。
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