**5. Relation of stomatal profiling with life histories**

opening and the rise in stomatal transpiration of the *syp121* mutant were delayed in the dark– light transition and following the Ca2+-evoked closure. The increase in stomatal density translates leads to an increase in *g*s and 30% greater *P*N under high light conditions [55]. Tanaka et al. [56] have used plants overexpressing STOMAGEN, a positive regulator of stomatal density, to produce transgenic plants with a two- to three fold greater stomatal density than the wild type. *P*<sup>N</sup> in these plants is increased by 30% due to greater CO2 diffusion into the leaf rather than changes in photosynthetic carboxylation capacity [56]. By contrast, some genes can induce low stomatal density and *g*<sup>s</sup> at high light intensities, for example, upregulation of *sdd1*

These findings exemplify the role of both the physical and functional stomatal features in determining *g*s. In particular, these works illustrate the importance of surrounding environ‐ mental conditions and ion exchange on stomatal behavior and the significance of examining

The analysis of evolution of stomata over species should depend on two strategies, i.e., fossil studies on ancestor plants and genetic studies on current plants. Fossil evidence shows that stomata have occurred in sporophytes and (briefly) gametophytes of embryophytes during the last 400 million years. Cladistic analyses with hornworts basal are consistent with a unique origin of stomata, although cladograms with hornworts as the deepest branching embryo‐

Genetic variation is a vital characteristic of every population that is required to adapt. Phenotypic trait variance within a population can be related to genetic variance as an estima‐

variation is attributable to genetic variance, the corresponded trait is highly heritable. Explor‐ ing stomatal traits with high *H* <sup>2</sup> under multiple environments could provide strategy for artificial selection and improvements on stomatal traits. Although natural variation in photosynthetic capacity especially stomatal features is known to exist among different species [59–63], relatively few studies have examined natural variation among accessions of the same species [64–67]. Besides, studying the genetic variation of photosynthetic capacity of different rice accessions with diverse genetic background could be an effective way to improve the

In fact, mining natural variations of photosynthetic and stomatal parameters is regarded as a promising approach to identify new genes or alleles for crop improvement. Conventionally, the identification of genomic loci that govern complex traits has been extensively facilitated by the development of quantitative trait locus (QTL) mapping approaches. Recent advances in high-throughput and high-dimensional genotyping and phenotyping technologies enable us to reduce the gaps between genomics and phenomics using the principles of genome-wide association studies (GWAS). This biostatistic method has been widely used in food crops for identifying genes that underlie natural variation of various ecological and agricultural traits

). In theory, when a greater proportion of phenotypic

phytes require loss of stomata early in the evolution of liverworts (reviewed by [58]).

can restrict CO2 diffusion limited *P*N to 80% of the wild type [57].

photosynthetic capacity of existing rice elite germplasm [67, 68].

tion of broad-sense heritability (*H* <sup>2</sup>

82 Applied Photosynthesis - New Progress

*g* s limitation on *P*N at fluctuating light and elevated CO2 and heat stress.

**4. Natural variation and heritability of stomatal conductance**

Evolutionary responses of stomata to fluctuating light conditions are important because stomata in theory must have been subject to evolutionary pressures associated with highly variable conditions. This is always related to the life history of accession origins. Studying the evolution of photosynthesis is critical to understand how stomata or plants structure variation influence ecological interactions and adaptation to various environments [74]. Where an overlying geographical origin or environmental gradient exerts strong adaptive selection, the natural variation in both genotype and phenotype is predicted. However, this variation will depend on the relative strength of selection, demographic history, and levels of dispersal and/ or gene flow among populations [75]. Differing selection pressures may include temperature, precipitation, and soil nutrient availability, growing season length, photoperiod, and biotic agents. Many of these factors are directly affected by geographic conditions and are therefore interrelated. This is already extensively reported in trees species. Genetic covariance among ecophysiological traits can be shaped by the past ecological and evolutionary processes [3]. However, for traits of ecological or evolutionary interest, studies must also address the extent to which population structure, trait variation, and genetic architecture covary along ecological gradients [3].
