Summer Warming Limited Bud Output Drives a Decline in Daughter Shoot Biomass through Reduced Photosynthetis of Parent Shoots in Leymus chinensis Seedlings

Understanding how summer warming influences the parent and daughter shoot production in a perennial clonal grass is vital for comprehending the response of grassland productivity to global warming.Here,we conducted a simulated experiment using potted Leymus chinensis,to study the relationship between the photosynthetic activ-ity of parent shoots and the production of daughter shoots under a whole(90 days)summer warming scenario(+3°C).The results showed that the biomass of parents and buds decreased by 25.52%and 33.45%,respectively,under warming conditions.The reduction in parent shoot biomass due to warming directly resulted from decreased leaf area(18.03%),chlorophyll a(18.27%),chlorophyll b(29.21%)content,as well as a reduction in net photosynthetic rate(7.32%)and the maximum quantum efficiency of photosystem II(PSII)photochemistry(4.29%).The decline in daughter shoot biomass was linked to a decrease in daughter shoot number(33.33%)by warming.However,the number of belowground buds increased by 46.43%.The results indicated that long-term summer warming reduces biomass accumulation in parent shoot by increasing both limitation of stoma and non-stoma.Consequently,the parent shoot allocates relatively more biomass to the belowground organs to maintain the survival and growth of buds.Overall,buds,as a potential aboveground population,could remedy for the cur-rent loss of parent shoot density by increasing the number of future daughter shoots if summer warming subsides.

Development and Age Structure of Ramets of Kalimeris integrifolia Populations in the Songnen Plains, Northeast China

Kalimeris integrifolia Turcz. is a root sucker form perennial herb of Compositae. In die late period of growing season, fresh fleshy radicels grow up above the soil surface to develop root-borne buds, which in turn grow into ramets and taproot. On the basis of observation on numerous samples, methods to classify the age of ramets and buds for the root sucker herbaceous plant population and to estimate the ages of taproots were established according to their morphology. The age of ramets was classified based on the regeneration times of taproot buds. Ramets developed from new root sucker buds were classified as 1 a. After 1 a ramets died, the ramets reproduced from the taproots were 2 a, and so on. New buds from a root sucker were 0 a buds, other age classes of buds were consistent with that of ramets, i.e. buds produced from taproots of I a ramets were 1 a buds, and so on. In the hay clipping meadows of the Songnen Plains, for K. integrifolia population, there are three age classes of ramets, representing a steady age structure. The maximal age of taproots of ramets is 4 a. Among all age classes, the population productivity of 2 a ramets was the highest, and that of I a ramets was the lowest. The ramet productivity increased with ramet age. During the early period of growing season, the productivity of 3 a ramets was the highest, but after the middle of growing season, I a ramets showed the greatest relative growth rate. The population size and age structure in the next year could be accurately forecasted by the number of fresh roots with budlet and present population in late autumn. The potential population in the bud banks was more than two times of the present population, which may provide sufficient substitution in the future.

The leaf size/number trade-off in herbaceous angiosperms

Aims In this study,we examined the extent to which between-species leaf size variation relates to variation in the intensity of leaf production in herbaceous angiosperms.Leaf size variation has been most commonly interpreted in terms of biomechanical constraints(e.g.affected by plant size limitations)or in terms of direct adaptation associated with leaf size effects in optimizing important physiological functions of individual leaves along environmental gradients(e.g.involving temperature and moisture).An additional interpretation is explored here,where adaptation may be more directly associated with the number of leaves produced and where relatively small leaf size then results as a trade-off of high‘leafing intensity’—i.e.number of leaves produced per unit plant body size.Methods The relationships between mean individual leaf mass,number of leaves and plant body size were examined for 127 species of herbaceous angiosperms collected from natural populations in southern Ontario,Canada.Important Findings In all,88%of the variation in mean individual leaf mass across species,spanning four orders of magnitude,is accounted for by a negative isometric(proportional)trade-off relationship with leafing intensity.These results parallel those reported in recent studies of woody species.Because each leaf is normally associated with an axillary bud or meristem,having a high leafing intensity is equivalent to having a greater number of meristems per unit body size—i.e.a larger‘bud bank’.According to the‘leafing intensity premium’hypothesis,because an axillary meristem represents the potential to produce either a new shoot or a reproductive structure,high leafing intensity should confer greater architectural and/or reproductive plasticity(with relatively small leaf size required as a trade-off).This greater plasticity,we suggest,should be especially important for smaller species since they are likely to suffer greater suppression of growth and reproduction from competition within multi-species vegetation.Accordingly,we tested and found support for the prediction that smaller species have not just smaller leaves generally but also higher leafing intensities,thus conferring larger bud banks,i.e.more meristems per unit plant body size.

Greater bud outgrowth of Bromus inermis than Pascopyrum smithii under multiple environmental conditions

Aims Tiller recruitment of perennial grasses in mixed-grass prairie primar-ily occurs from belowground buds.Environmental conditions,such as temperature,soil moisture and grazing can affect bud outgrowth of both invasive and native perennial grasses.Differential bud out-growth responses of native and invasive species to climate change and grazing could alter competitive interactions that have impli-cations for future land management.The aims of this work were to(i)compare how spring temperature altered bud outgrowth of native Pascopyrum smithii(Rydb.)Á.Löve(western wheatgrass)and introduced Bromus inermis Leyss.(smooth brome),(ii)compare how watering frequency altered bud outgrowth of these two species and(iii)evaluate how clipping interacts with spring temperature or watering frequency to affect P.smithii bud outgrowth.Methods Individual plants of B.inermis and P.smithii were harvested from North American mixed-grass prairie.Bud outgrowth from tillers of both species were evaluated under three spring temperature regimes(Average:12,18 and 24°C)and two watering frequen-cies(frequent and intermittent)in a growth chamber experiment.The response of P.smithii bud outgrowth to clipping was also examined.Important Findings Bromus inermis had more buds per tiller and initiated a greater pro-portion of these buds than P.smithii under all temperature and mois-ture conditions.Pascopyrum smithii bud development was reduced at 24°C.Intermittent watering did not significantly impact bud out-growth of either species.Clipping increased P.smithii bud mortality and reduced its bud development for the 2-week period of the study.The robust vegetative reproductive capacity of B.inermis under a range of environmental conditions is a key mechanism enabling the expansion of B.inermis into P.smithii-dominated mixed-grass prai-rie in North America.Mixed-grass prairie dominated by P.smithii experiencing repeated defoliation may require longer recovery times and be more susceptible to B.inermis invasion due to the negative impact of grazing on P.smithii bud outgrowth.Successful tiller recruitment and establishment of native perennial grasses via the bud bank will be necessary for mixed-grass prairie to be resilient to climate change,plant invasions and grazing.

Leaf size versus leaf numbertradeoffs in dioecious angiosperms

Aims We explore the possible role of leaf size/number trade-offs for the interpretation of leaf size dimorphism in dioecious plant species.Methods Total above-ground biomass(both male and female)for three herbaceous dioecious species and individual shoots(from both male and female plants)for three woody dioecious species were sampled to record individual leaf dry mass,number of leaves,dry mass of residual above-ground tissue(all remaining non-leaf biomass),number of flowers/inflorescences(for herbaceous species)and number of branches.Important Findings For two out of three woody species and two out of three herbaceous species examined,male plants produced smaller leaves but with higher leafing intensity—i.e.more leaves per unit of supporting(residual)shoot tissue or plant body mass—compared with females.Male and female plants,however,did not differ in shoot or plant body mass or branching intensity.We interpret these results as possible evidence for a dimorphic leaf deployment strategy that promotes both male and female function,respectively.In male plants,capacity as a pollen donor may be favored by selection for a broadly spaced floral display,hence favoring relatively high leafing intensity because this provides more numerous axillary meristems that can be deployed for flowering,thus requiring a relatively small leaf as a trade-off.In one herbaceous species,higher leafing intensity in males was associated with greater flower production than in females.In contrast,in female plants,selection favors a relatively large leaf,we propose,because this promotes greater capacity for localized photosynthate production,thus supporting the locally high energetic cost of axillary fruit and seed development,which in turn requires a relatively low leafing intensity as a trade-off.

No evidence of a generalized potential ‘cost’ of apical dominance for species that have strong apical dominance

When the shoot apical meristem of plants is damaged or removed,fecundity and/or plant growth may suffer(under-compensation),remain unaffected(compensation)or increase(overcompensation).The latter signifies a potential‘cost’of apical dominance.Using natural populations of 19 herbaceous angiosperm species with a conspicuously vertical,apically dominant growth form,we removed(clipped)the shoot apical meristem for replicate plants early in the growing season to test for a potential cost of apical dominance.Clipped and unclipped(control)plants had their near neighbours removed,and were harvested after flowering production had finished but before seed dispersal.Dry mass was measured separately for aboveground body size(shoots),leaves,seeds and fruits;and number of leaves,fruits and seeds per plant were counted.We predicted that:(i)our study species(because of their strong apically dominant growth form)would respond to shoot apical meristem removal with greater branching intensity,and thus overcompensation in terms of fecundity and/or biomass;and(ii)overcompensation is particularly enabled for species that produce smaller but more leaves,and hence with a larger bud bank of axillary meristems available for deployment in branching and/or fruit production.Widely variable compensatory capacities were recorded,and with no significant between-species relationship with leaf size or leafing intensity—thus indicating no generalized potential cost of apical dominance.Overall,the results point to species-specific treatment effects on meristem allocation patterns,and suggest importance for effects involving local variation in resource availability,and between-species variation in phenology,life history traits and susceptibility to herbivory.