Changes in leaf stomatal traits of different aged temperate forest stands

Stomata control carbon and water vapor exchange between the leaves and the atmosphere,thus infl uencing photosynthesis and transpiration.Combinations of forest patches with different stand ages are common in nature,however,information of which stomatal traits vary among these stands and how,remains limited.Here,seven different aged forest stands(6,14,25,36,45,55,and 100 years)were selected in typical temperate,mixed broadleaf-conifer forests of northeast China.Stomatal density,size and relative area of 624 species,including the same species in stands of different ages were selected.Stomatal density,size and relative area were distributed log-normally,differing across all species and plant functional groups.Stomatal density ranged from 4.2 to 1276.7 stomata mm^(–2),stomatal size ranged from 66.6 to 8315.7μm^(2),and stomatal relative area 0.1–93.3%.There was a significant negative relationship between density and size at the species and functional group levels,while the relative stomatal area was positively correlated with density and size.Stomatal traits of dominant species were relatively stable across different stand ages but were significantly different for herbs.The results suggest that stomatal traits remain relatively stable for dominant species in natural forests and therefore,spatial variation in stomatal traits across forest patches does not need to be incorporated in future ecological models.

Plant ontogenetic changes in vein and stomatal traits and their relationship with economic traits in leaves of three Mediterranean oaks

Aims We compared vein and stomatal traits of seedlings and adults of three Mediterranean Quercus species.Previous work suggests that gas-exchange rates tend to be higher at the seedling stage than in adults.Our objective was to determine whether vein and stomatal traits vary throughout whole-plant ontogeny in parallel with the changes in gas-exchange rates.We addressed the following alternative hypotheses:hypothesis 1—seedlings show higher vein and stomatal densities than adults;and hypothesis 2—seedlings have lower investments in vascular tissues to reduce construction costs.Methods Ten specimens from each growth stage were randomly sampled for each species in a location in central-western Spain.We measured mean stomatal and vein traits(size and number of stomata per unit of leaf area,vein density,vein volume,vein to epidermis distance),leaf mass per area and lamina thickness.Important Findings Minor vein density and vein volume per area increased with tree age,which seems inconsistent with the ontogenetic trends in gas-exchange rates.This discrepancy is in support of our hypothesis 2,and it suggests that,at the seedling stage,reducing investments in vascular tissues in benefit of maximizing growth rates is a priority.Larger interveinal distances in seedlings were compensated by smaller vein to epidermis distances.The thin leaves of the seedlings may thus constitute as a necessary trait for achieving shorter path length distances for the transport of water to evaporation sites without the need for a strong investment in costly vascular tissues.

Mapping QTLs for stomatal density and size under drought stress in wheat(Triticum aestivum L.)

Stomatal density and size affect plant water use efficiency, photosynthsis rate and yield. The objective of this study was to gain insights into the variation and genetic basis of stomatal density and size during grain filling under drought stress（DS） and well-watered（WW） conditions. The doubled haploid population derived from a cross of wheat cultivars Hanxuan 10（H10）, a female parent, and Lumai 14（L14）, a male parent, was used for phenotyping at the heading, flowering, and mid- and late grain filling stages along with established amplified fragment length polymorphism（AFLP） and simple sequence repeat（SSR） markers. The stomatal density of doubled haploid（DH） lines was gradually increased, while the stomatal lengths and widths were gradually decreased during grain filling stage. Twenty additive QTLs and 19 pairs of epistatic QTLs for the 3 traits were identified under DS. The other 20 QTLs and 25 pairs epistatic QTLs were obtained under WW. Most QTLs made more than 10% contributions to the total phenotypic variations at one growth stage under DS or WW. Furthermore, QTLs for stomatal density near Xwmc74 and Xgwm291 located on chromosome 5A were tightly linked to previously reported QTLs regulating total number of spikelets per spike, number of sterile spikelets per spike and proportion of fertile spikelets per spike. Qsw-2D-1 was detected across stages, and was in the same marker region as a major QTL for plant height, QPH.cgb-2D.1. These indicate that these QTLs on chromosomes 5A and 2D are involved in regulating these agronomic traits and are valuable for molecular breeding.

Photosynthetic response dynamics in the invasive species Tithonia diversifolia and two co-occurring native shrub species under fluctuating light conditions

To determine the invasiveness of invasive plants,many studies have compared photosynthetic traits or strategies between invasive and native species.However,few studies have compared the photosynthetic dynamics between invasive and native species during light fluctuations.We compared photosynthetic induction,relaxation dynamics and leaf traits between the invasive species,Tithonia diversifolia and two native species,Clerodendrum bungei and Blumea balsamifera,in full-sun and shady habitats.The photosynthetic dynamics and leaf traits differed among species.T.diversifolia showed a slower induction speed and stomatal opening response but had higher average intrinsic water-use efficiency than the two native species in full-sun habitats.Thus,the slow induction response may be attributed to the longer stomatal length in T.diversifolia.Habitat had a significant effect on photosynthetic dynamics in T.diversifolia and B.balsamifera but not in C.bungei.In shady habitat,T.diversifolia had a faster photosynthetic induction response than in full-sun habitat,leading to a higher average stomatal conductance during photosynthetic induction in T.diversifolia than in the two native species.In contrast,B.balsamifera had a larger stomatal length and slower photosynthetic induction and relaxation response in shady habitat than in full-sun habitat,resulting in higher carbon gain during photosynthetic relaxation.Nevertheless,in both habitats,T.diversifolia had an overall higher carbon gain during light fluctuations than the two native species.Our results indicated that T.diversifolia can adopt more effective response strategies under fluctuating light environments to maximize carbon gain,which may contribute to its successful invasion.

Spatio-temporal variation in transpiration responses of maize plants to vapor pressure deficit under an arid climatic condition

The transpiration rate of plant is physically controlled by the magnitude of the vapor pressure deficit（VPD） and stomatal conductance. A limited-transpiration trait has been reported for many crop species in different environments, including Maize（Zea mays L.）. This trait results in restricted transpiration rate under high VPD, and can potentially conserve soil water and thus decrease soil water deficit. However, such a restriction on transpiration rate has never been explored in maize under arid climatic conditions in northwestern China. The objective of this study was to examine the transpiration rate of field-grown maize under well-watered conditions in an arid area at both leaf and whole plant levels, and therefore to investigate how transpiration rate responding to the ambient VPD at different spatial and temporal scales. The transpiration rates of maize at leaf and plant scales were measured independently using a gas exchange system and sapflow instrument, respectively. Results showed significant variations in transpiration responses of maize to VPD among different spatio-temporal scales. A two-phase transpiration response was observed at leaf level with a threshold of 3.5 k Pa while at the whole plant level, the daytime transpiration rate was positively associated with VPD across all measurement data, as was nighttime transpiration response to VPD at both leaf and whole plant level, which showed no definable threshold vapor pressure deficit, above which transpiration rate was restricted. With regard to temporal scale, transpiration was most responsive to VPD at a daily scale, moderately responsive at a half-hourly scale, and least responsive at an instantaneous scale. A similar breakpoint（about 3.0 k Pa） in response of the instantaneous leaf stomatal conductance and hourly canopy bulk conductance to VPD were also observed. At a daily scale, the maximum canopy bulk conductance occurred at a VPD about 1.7 k Pa. Generally, the responsiveness of stomatal conductance to VPD at the canopy scale was lower than that at leaf scale. These results indicate a temporal and spatial heterogeneity in how maize transpiration responses to VPD under arid climatic conditions. This could allow a better assessment of the possible benefits of using the maximum transpiration trait to improve maize drought tolerance in arid environment, and allow a better prediction of plant transpiration which underpin empirical models for stomatal conductance at different spatio-temporal scales in the arid climatic conditions.