Biochemical and anatomical leaf characteristics of oak trees contribute to differences in photosynthetic capacity between leaf habits

Plant life-history strategies associated with resource acquisition and economics (e.g. leaf habit) are thought to be fundamental determinants of the traits and mechanisms that drive herbivore pressure, resource allocation to plant defensive traits, and the simultaneous expression (positive correlations) or trade-offs (negative correlations) between these defensive traits. In particular, it is expected that evergreen species - which usually grow slower and support constant herbivore pressure in comparison with deciduous species - will exhibit higher levels of both physical and chemical defences and a higher predisposition to the simultaneous expression of physical and chemical defensive traits. Here, by using a dataset which included 56 oak species (Quercus genus), we investigated whether leaf habit of plant species governs the investment in both physical and chemical defences and pair-wise correlations between these defensive traits. Our results showed that leaf habit does not determine the production of most leaf physical and chemical defences. Although evergreen oak species had higher levels of leaf toughness and specific leaf mass (physical defences) than deciduous oak species, both traits are essentially prerequisites for evergreenness. Similarly, our results also showed that leaf habit does not determine pair-wise correlations between defensive traits because most physical and chemical defensive traits were simultaneously expressed in both evergreen and deciduous oak species. Our findings indicate that leaf habit does not substantially contribute to oak species differences in plant defence investment.

Water and nutrient application using three irrigation systems, namely daily drip irrigation, pulsing drip irrigation and micro irrigation were studied with respect to photosynthetic efficiency, water use efficiency and leaf water relations in ‘Brookfield Gala’ apple trees during 2004/5 and 2005/6 in the Western Cape Province, South Africa. The amount of water used per irrigation strategy was 5254 m3 ha−1 yr−1 and 5661 m3 ha−1 yr−1 for the micro irrigation; 3429 m3 ha−1 yr−1 and 39260 m3 ha−1 yr−1 for the daily drip and 3429 m3 ha−1 yr−1 and 4047 m3 ha−1 yr−1 for the pulsing drip for 2004/5 and 2005/6 seasons respectively. Trees were budded on either M793 or M7 root-stocks and planted in blocks using a split-plot experimental design with irrigation as the main effect and root-stock as the sub-plot. Maximum light-saturated net CO2 assimilation rate (Amax) was consistently higher under pulsing drip irrigation (this system applies water several times during the day creating an even shorter frequency cycle than the normal daily drip) compared to micro irrigation (applies water once to twice a week and uses sprinklers that spray water in a circle resulting in wetting a continuous strip within the drip row) but, occasionally, significantly higher than daily drip irrigation (applies water on a daily basis creating a shorter cycle compared to micro sprinkler system). The maximum rate of electron transport (Jmax) showed similar trends to Amax during 2004/5, but not during 2005/6. Amax peaked during midmorning (10h00) with a steady decline thereafter in all treatments, but with significantly lower rates under micro irrigation. Stomatal conductance (gs) declined steadily throughout the morning, with higher gs under the drip based systems compared to the micro system. The implications are that, irrigation application should be given early in the morning to sustain stomatal conductance and maximise CO2 assimilation rates during the period between 08h00 to 12h00. Results indicate higher photosynthetic capacity and water use efficiency under both drip-based irrigation systems compared to micro irrigation. Differences in photosynthetic capacity were related to both stomatal and non-stomatal responses.

Interactions between leaf traits and environmental factors help explain the growth of evergreen and deciduous species in a subtropical forest

Within-branch photosynthetic gradients are more related to the coordinated investments of nitrogen and water than leaf mass per area

Leaf habit is a major axis of plant diversity that has consequences for carbon balance since the leaf is the primary site of photosynthesis. Nonstructural carbohydrates (NSCs) produced by photosynthesis can be allocated to storage and serve as a resiliency mechanism to future abiotic and biotic stress. However, how leaf habit affects NSC storage in an evolutionary context has not been shown. Using a comparative physiological framework and an analysis of evolutionary model fitting, we examined if variation in NSC storage is explained by leaf habit. We measured sugar and starch concentrations in 51 oak species (Quercus spp.) growing in a common garden and representing multiple evolutions of three different leaf habits (deciduous, brevideciduous and evergreen). The best fitting evolutionary models indicated that deciduous oak species are evolving towards higher NSC concentrations than their brevideciduous and evergreen relatives. Notably, this was observed for starch (the primary storage molecule) in the stem (a long-term C storage organ). Overall, our work provides insight into the evolutionary drivers of NSC storage and suggests that a deciduous strategy may confer an advantage against stress associated with a changing world. Future work should examine additional clades to further corroborate this idea.

Dry seasonal ecosystems such as the Florida sandhill are defined by a pronounced and consistent dry season that results in both water and nutrient limitation. Deciduous and evergreen species have evolved different leaf phenologies, which change the temporal pattern of nutrient demands for leaf growth. To measure N uptake for deciduous and evergreen species during late dry season deciduous leaf-out, we labeled the shallow soil with 15N by spreading a mixture of native sand and 15N-KNO3 around each tree and measured foliar nitrogen isotopic composition. We also measured foliar N content and nitrogen resorption efficiency (NRE). Evergreen and deciduous species were not consistently different in foliar N content and NRE, but natural foliar δ15N values were consistently higher in deciduous species. Labeling experiments show that uptake rate of 15N- labeled NO3 − was lowest for the deciduous species. Inconsistent results in foliar N content and NRE do not explain the differences in leaf habit in nutrient-poor ecosystems. Low N uptake during leaf-out limits deciduous species to the most fertile regions of the Florida scrub as well as in several other ecosystems, so that they can take up sufficient N to meet the demands of leaf growth.

This study was conducted to determine the carbon (C) contents in different mixed stands of P. densiflora and deciduous oak species in Gwangneung, central Korea. Five mixed stands with different ratios of P. densiflora and deciduous oak species were chosen based on the basal area of all trees ≥5 cm DBH: pure P. densiflora (P100D0), 70% P. densiflora+30% deciduous oak species (P70D30), 44% P. densiflora+56% deciduous oak species (P50D50), 37% P. densiflora+63% deciduous oak species (P40D60), and 10% P. densiflora+90% deciduous oak species (P10D90). Total C contents in the overstory (aboveground and belowground) vegetation were higher in the mixed stands (P70D30, P50D50, P40D60) than in the pure stands (P100D0, P10D90). Moreover, except for P40D60, C contents of forest floor (litter and coarse woody debris) were larger in the mixed stands (P70D30, P50D50) than in the pure stands. However, total soil C contents up to 30cm depth were highest in the pure deciduous oak stand than in the pure P. densiflora stand and mixed stands. Total ecosystem C contents (Mg/ha) were 163.3 for P100D0, 152.3 for P70D30, 188.8 for P50D50, 160.2 for P40D60, and 150.4 for P10D90, respectively. These differences in total ecosystem C contents among the different mixed stands for P. densiflora and deciduous oak species within the study stands were attributed by the differences in vegetation development and forest management practices. Among the five study stands, the total ecosystem C contents were maximized in the 1:1 mixed ratio of P. densiflora and deciduous oak species (P50D50).

In evergreen plants, old leaves may contribute photosynthate to initiation of shoot growth in the spring. They might also function as storage sites for carbohydrates and nitrogen (N). We hence hypothesized that whole-plant allocation of carbohydrates and N to storage in stems and roots may be lower in evergreen than in deciduous species. We selected three species pairs consisting of an evergreen and a related deciduous species: Mahonia aquifolium (Pursh) Nutt. and Berberis vulgaris L. (Berberidaceae), Prunus laurocerasus L. and Prunus serotina Ehrh. (Rosaceae), and Viburnum rhytidophyllum Hemsl. and Viburnum lantana L. (Adoxaceae). Seedlings were grown outdoors in pots and harvested on two dates during the growing season for the determination of biomass, carbohydrate and N allocation ratios. Plant size-adjusted pools of nonstructural carbohydrates in stems and roots were lower in the evergreen species of Berberidaceae and Adoxaceae, and the slope of the carbohydrate pool vs plant biomass relationship was lower in the evergreen species of Rosaceae compared with the respective deciduous species, consistent with the leading hypothesis. Pools of N in stems and roots, however, did not vary with leaf habit. In all species, foliage contained more than half of the plant's nonstructural carbohydrate pool and, in late summer, also more than half of the plant's N pool, suggesting that in juvenile individuals of evergreen species, leaves may be a major storage site. Additionally, we hypothesized that concentration of defensive phenolic compounds in leaves should be higher in evergreen than in deciduous species, because the lower carbohydrate pool in stems and roots of the former restricts their capacity for regrowth following herbivory and also because of the need to protect their longer-living foliage. Our results did not support this hypothesis, suggesting that evergreen plants may rely predominantly on structural defenses. In summary, our study indicates that leaf habit has consequences for storage economics at the whole-plant level, with evergreen shrub species storing less carbohydrates (but not N) per unit plant biomass than deciduous species.

Leaf habit does not predict leaf functional traits in cerrado woody species

Leaf chlorophyll content is positively associated with photosynthetic capacity and nutrient status, but its functional ecology has seldom been examined thus far. In the present study, we measured leaf chlorophyll and carotenoid concentrations, determined chlorophyll a : chlorophyll b (Chl a : Chl b) and carotenoids : chlorophyll ratios and measured leaf mass per area (LMA) for 63 woody dicot species, including 24 evergreen species and 39 deciduous species, at two altitudes (1800–2400 and 2400–2800 m a.s.l.) of Gongga Mountain, south-west China. The aim of the present study was to determine whether evergreen and deciduous species differ in terms of leaf pigment concentrations and LMA in response to environmental differences associated with changes in elevation. In both life forms, the altitude effect was not significant for chlorophyll and carotenoid concentrations. However, the Chl a : Chl b ratio was significantly higher in evergreen species, whereas LMA was significantly higher in deciduous species, at the high versus low altitude. These observations suggest that evergreen and deciduous species may have different strategies to protect leaf pigments. Mass-based leaf pigment concentrations were lower in evergreen compared with deciduous species, especially at high altitude. LMA was higher in evergreen than deciduous species at both altitudes. Pigment concentrations were negatively correlated with LMA in both life forms at both altitudes. The slope of LMA vs mass-based leaf pigment concentrations was significantly more negative for deciduous than evergreen species, and at low versus high altitude for deciduous species. The findings suggest that deciduous species may invest less photosynthate in leaf pigments but more in inactive components in stressful environments than do evergreens. Thus, the same magnitude of variation in LMA may have different consequences on leaf carbon balance between evergreen and deciduous species, which helps explain why evergreen species are often more likely to occupy more stressful environments than deciduous species.

BackgroundLeaf stomatal conductance is an important indicator of photosynthetic capacity. However, stomatal conductance is poorly quantified and rarely explored in the context of the leaf functional traits for epiphytes, particularly when it comes to herbaceous species with different leaf habits (deciduous vs. deciduous species). Here, we investigated leaf stomatal conductance, leaf dry mass per unit area, leaf thickness, stomatal density, abaxial epidermal cell size and pigment contents in 23 Dendrobium evergreen and deciduous species from a greenhouse. Our main objectives were to compare differences in all measured traits between evergreen and deciduous species, and to determine the relationships of leaf stomatal conductance with leaf functional traits and leaf pigments.ResultsThe results showed that the evergreen species of Dendrobium had thicker leaves and higher leaf dry mass per unit area, whereas deciduous species had higher leaf stomatal conductance and higher leaf chlorophyll contents. Leaf stomatal conductance had a negative correlation with leaf thickness, and dry mass per unit area, but a positive correlation with leaf pigment contents. There was a negative correlation between pigment contents and leaf dry mass per unit area.ConclusionThe results reveal the clear differences in leaf stomatal conductance, leaf functional traits and leaf pigments between deciduous and evergreen Dendrobium species, with the form groups showing trait values indicative of less investments in structural components and of more investments in photosynthetic carbon gain. Furthermore, leaf dry mass per unit area and leaf pigments play an important role in shaping leaf stomatal conductance.

Leaf respiration in the light (Rlight) is crucial for understanding the net CO2 exchange of individual plants and entire ecosystems. However, Rlight is poorly quantified and rarely discussed in the context of the leaf economic spectrum (LES), especially among woody species differing in plant functional types (PFTs) (e.g., evergreen vs. deciduous species). To address this gap in our knowledge, Rlight, respiration in the dark (Rdark), light-saturated photosynthetic rates (Asat), leaf dry mass per unit area (LMA), leaf nitrogen (N) and phosphorus (P) concentrations, and maximum carboxylation (Vcmax) and electron transport rates (Jmax) of 54 representative subtropical woody evergreen and deciduous species were measured. With the exception of LMA, the parameters quantified in this study were significantly higher in deciduous species than in evergreen species. The degree of light inhibition did not significantly differ between evergreen (52%) and deciduous (50%) species. Rlight was significantly correlated with LES traits such as Asat, Rdark, LMA, N and P. The Rlight vs. Rdark and N relationships shared common slopes between evergreen and deciduous species, but significantly differed in their y-intercepts, in which the rates of Rlight were slower or faster for any given Rdark or N in deciduous species, respectively. A model for Rlight based on three traits (i.e., Rdark, LMA and P) had an explanatory power of 84.9%. These results show that there is a link between Rlight and the LES, and highlight that PFTs is an important factor in affecting Rlight and the relationships of Rlight with Rdark and N. Thus, this study provides information that can improve the next generation of terrestrial biosphere models (TBMs).

Deciduous species of Nothofagus tend to replace evergreen Nothofagus at the highest altitudes. We investigated whether deciduous Nothofagus species have higher maximum rates of net photosynthesis (Pmax) and specific leaf area (SLA) than evergreen species and whether there is an increasing photosynthetic advantage (e.g. higher Pmax) in deciduous species relative to evergreen species with increasing altitude that might explain their replacement of evergreen species. Net photosynthesis was investigated in (1) five deciduous and five evergreen species of Nothofagus grown in a common environment and (2) two co-occurring species, N. gunnii (Hook.f.) Oerst. (deciduous) and N. cunninghamii (Hook.) Oerst. (evergreen), across a range of altitudes in Tasmania. In the first experiment, the maximum rate of net photosynthesis per leaf mass (Pmax, mass) and SLA were higher in deciduous species, whereas the maximum rate of net photosynthesis per leaf area (Pmax, area) did not differ between leaf habits. However, in the field-based study, both mass- and area-based Pmax were higher in N. gunnii than N. cunninghamii across all sites. The high Pmax, mass of deciduous species may provide a competitive advantage at higher altitudes by maximising carbon gain during the growing season. However, in the study of sympatric populations of N. gunnii and N. cunninghamii there was no evidence of increasing photosynthetic advantage of the deciduous N. gunnii with increasing altitude.

Different responses to shade of evergreen and deciduous oak seedlings and the effect of acorn size

AimEvergreen and deciduous broadleaved plants have long been considered as different strategies to cope with environmental conditions, which are closely related to the trait syndromes associated with leaf habits. However, there are no assessments of differences in functional diversity among evergreen and deciduous species over a regional scale.LocationSubtropical evergreen broadleaved forest (SEBLF) of China.MethodsWe measured seven functional traits of 292 woody plant species in 250 forest plots across five locations in the SEBLF. We quantified functional richness (FRic), functional divergence (FDiv), and functional evenness (FEve) for evergreen vs deciduous species separately. We compared the patterns of variation of functional diversity for different leaf habits along geographical (latitude, longitude and elevation) and environmental (climate and soil) gradients.ResultsFunctional richness of evergreen species was higher than that of deciduous species, while FDiv and FEve were lower. FRic of evergreen species decreased while FDiv increased with increasing elevation. For deciduous species, FRic and FDiv decreased with increasing latitude. With the increase of longitude, only FDiv of evergreen species decreased. FEve of both leaf habits did not exhibit geographical patterns. Environmental variables explained 9%–38% and 4%–33% of the variation in functional diversity of evergreen and deciduous species respectively. The temperature range was the most important factor affecting FRic and FDiv of evergreen species, while FRic of deciduous species was mainly affected by precipitation of the driest quarter. FEve of both leaf habits was mostly affected by soil conditions.Main conclusionsFunctional diversity of subtropical forests in China revealed different geographical patterns across leaf habits. The functional diversity of evergreen species was mainly linked to temperature, while the deciduous species were driven by precipitation. Our study demonstrated that different functional diversity patterns of evergreen and deciduous broadleaved plants in response to environment can result in the coexistence of the two leaf habit types.