我不会用专业工具查论文（声明一下偶是工科，羞愧一下），只好放狗试了一下，查到这篇短文。估计英文的科普可信度比中文高一些。这篇短文好像是说（英文水平不高有错望海涵）植物光合作用的实际效率在1%到2%之间，甘蔗的效率最高，达8%。很多植物的效率只有0.1%。

下面是短文相应的一段：

Photosynthesis is the most important biological process on Earth. It serves as the World's largest solar battery. The primary reactions have close to 100% quantum efficiency (i.e., one quantum of light leads toone electron transfer); and under most ideal conditions, the overall energy efficiency can reach 35%. Due to losses at all steps in biochemistry, one has been able to get only about 1 to 2% energy efficiency in most crop plants. Sugarcane is an exception as it can have almost 8% efficiency. However, many plants in Nature often have only 0.1 % energy efficiency.

短文地址：

http://www.life.uiuc.edu/govindjee/whatisit.htm

短文提到的相应参考书在狗狗图书馆的地址：

http://books.google.com/books?id=y1Nb7EvZ7iAC&printsec=frontcover&dq=Energy,+Plants+and+Man&sig=wMlpPHZ0vhLMVm4M-S17t9pXb9Q

继续放狗，查到些貌似论文的咚咚，但是问题又来了，偶看不懂这些论文在说什么。它们没有直接说photosynthesis efficiency 或者rate是多少。找到一章图表，仍然看不懂。貌似这些论文讨论的不是如何“提高水稻的光合作用效率”，而是讨论“提高水稻的水或者是氮的利用效率”。偶基本摸不着头脑，希望专家出现。

http://www.irri.cgiar.org/publications/wrrc/wrrcPDF/session4-01.pdf

http://www.plantphysiol.org/cgi/content/full/130/4/1999