More radiation generally increases vegetation photosynthesis, but field studies show that a given amount of diffuse radiation leads to more fixed carbon than direct radiation.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/impact-changes-diffuse-radiation-global-land-carbon-sink
[2] http://admin.indiaenvironmentportal.org.in/category/author/lina-m-mercado
[3] http://admin.indiaenvironmentportal.org.in/category/author/nicolas-bellouin
[4] http://admin.indiaenvironmentportal.org.in/category/author/stephen-sitch-et-al
[5] http://admin.indiaenvironmentportal.org.in/category/journal/nature
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/forests
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-change
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-science
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/aerosols
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/carbon-sinks
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/radiation