Why are there so few C2 grasses?

绝大多数植物都使用C3光合作用。然而，一种被称为C4的涡轮增压光合作用形式在近70个谱系中独立进化，并被我们最多产的食物和生物能源作物所使用。C4光合作用通过对叶片生物化学和解剖结构的一系列修改，从祖先的C3型反复进化，这不可避免地产生了C3和C4状态之间的进化中间产物。这些C3-C4中间体使用一种罕见的生理机能，叫做C2光合作用。C4光合作用在禾草中独立进化了20多次，产生了大量的C4禾草物种（约4500个）。尽管如此，只有不到10种C2草被确定。如果C2光合作用是C4创新的重要中间步骤，那么为什么C2草那么少呢？也许C2草实际上很常见，但迄今为止发现的很少。或者，过去丰富的C2草可能已经灭绝了。另一种可能性是，C4光合作用的出现可能在一些谱系中绕过了C2中间状态，并通过不同的、目前未知的进化路径进化。这个学生将通过在生态和系统地理背景下调查草的光合多样性来了解C4光合作用是如何在草中出现的，从而试图确定为什么C2草如此之少。为此，学生将在阿根廷进行实地考察，并在班戈大学和邱园植物标本室进行定制培训的同时，接受植物表型、实地考察、系统发育和公共馆藏利用方面的培训

The vast majority of plant species use C3 photosynthesis. However, a turbo-charged form of photosynthesis called C4 evolved independently in nearly 70 lineages and is used by our most productive food and bioenergy crops. C4 photosynthesis evolved repeatedly from the ancestral C3 type via a series of modifications to leaf biochemistry and anatomy, which inevitably created evolutionary intermediates between C3 and C4 states. These C3-C4 intermediates use a rare physiology called C2 photosynthesis. C4 photosynthesis evolved independently over 20 times in the grasses, yielding a remarkable number of C4 grass species (~4500). Despite this, fewer than 10 C2 grass species have been identified. If C2 photosynthesis is an important intermediary step in C4 innovation, then why are there so few C2 grasses?Perhaps C2 grasses are actually common, but few have been identified to date. Alternatively, abundant C2 grasses of the past may have since become extinct. Another possibility is that the emergence of C4 photosynthesis may circumvent the C2 intermediate state in some lineages and evolve via different, currently unknown, evolutionary paths.This studentship will seek to identify why there are so few C2 grasses by investigating grass photosynthetic diversity within an ecological and phylogeographical context to understand how C4 photosynthesis emerged in the grasses. To do this, the student will train in plant phenotyping, fieldwork, phylogenetics, and use of public collections while undertaking fieldwork in Argentina and customized training at the University of Bangor and Kew Herbarium