Costs and benefits of photosynthetic stems in desert species from southern California

Woody plants with green photosynthetic stems are common in dry woodlands with the possible advantages of extra carbon gain, re-assimilation of CO2, and high water-use efficiency. However, their green stem tissue may also incur greater costs of water loss when stomata are closed. Our study focussed on evaluating the costs and benefits of having green stems in desert plants, addressing the water-use efficiency hypothesis. We measured water status, carbon and water exchange, and carbon, nitrogen and oxygen isotopic composition of 15 species in a desert wash scrub in Joshua Tree National Park, California, USA. We found that all woody species that have green stems relied on their green stems as the sole organ for carbon assimilation for most of the study period. Green stems had similar photosynthetic rate (Amax), stomatal conductance (gs) and intrinsic water-use efficiency (WUEi) to leaves of the same species. However, Amax, gs and cuticular conductance (gmin) were higher in green stems than in leaves of non-green stemmed species. Carbon isotopic composition (δ13C) was similar in both leaves and green stems, indicating no difference in integrated long-term WUE. Our results raise questions about the possible trade-off between carbon gain and water loss through the cuticle in green stems and how this may affect plant responses to current and future droughts.

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Plant Responses to Salinity Under Elevated Atmospheric Concentrations of CO2

Australian Journal of Botany ◽

10.1071/bt9920515 ◽

1992 ◽

Vol 40 (5) ◽

pp. 515 ◽

Cited By ~ 49

Author(s):

MC Ball ◽

R Munns

Keyword(s):

Water Use Efficiency ◽

Elevated Co2 ◽

Water Use ◽

Water Loss ◽

Salt Flux ◽

Carbon Gain ◽

Salt Balance ◽

Salt Uptake ◽

Use Efficiency ◽

Atmospheric Concentrations

This review explores effects of elevated CO2 concentrations on growth in relation to water use and salt balance of halophytic and non-halophytic species. Under saline conditions, the uptake and distribution of sodium and chloride must be regulated to protect sensitive metabolic sites from salt toxicity. Salt-tolerant species exclude most of the salt from the transpiration stream, but the salt flux from a highly saline soil is still considerable. To maintain internal ion concentrations within physiologically acceptable levels, the salt influx to leaves must match the capacities of leaves for salt storage and/or salt export by either retranslocation or secretion from glands. Hence the balance between carbon gain and the expenditure of water in association with salt uptake is critical to leaf longevity under saline conditions. Indeed, one of the striking features of halophytic vegetation, such as mangroves, is the maintenance of high water use efficiencies coupled with relatively low rates of water loss and growth. These low evaporation rates are further reduced under elevated CO2 conditions. This, with increased growth, leads to even higher water use efficiency. Leaves of plants grown under elevated CO2 conditions might be expected to contain lower salt concentrations than those grown under ambient CO2 if salt uptake is coupled with water uptake. However, salt concentrations in shoot tissues are similar in plants grown under ambient and elevated CO2 conditions despite major differences in water use efficiency. This phenomenon occurs in C3 halophytes and in both C3 and C2 non-halophytes. These results imply shoot/root communication in regulation of the salt balance to adjust to environmental factors affecting the availability of water and ions at the roots (salinity) and those affecting carbon gain in relation to water loss at the leaves (atmospheric concentrations of water vapour and carbon dioxide).

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Water-Use Efficiency and Carbon Isotopic Composition in Reduced Tillage Systems

Soil Science Society of America Journal ◽

10.2136/sssaj1999.03615995006300020013x ◽

1999 ◽

Vol 63 (2) ◽

pp. 356-361 ◽

Cited By ~ 10

Author(s):

F. L. Walley ◽

A. Matus ◽

G. P. Lafond ◽

C. van Kessel

Keyword(s):

Isotopic Composition ◽

Water Use Efficiency ◽

Water Use ◽

Carbon Isotopic Composition ◽

Reduced Tillage ◽

Tillage Systems ◽

Carbon Isotopic ◽

Use Efficiency

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Impact of Climate, Stand Growth Parameters, and Management on Isotopic Composition of Tree Rings in Chestnut Coppices

Forests ◽

10.3390/f10121148 ◽

2019 ◽

Vol 10 (12) ◽

pp. 1148 ◽

Cited By ~ 2

Author(s):

Francesco Marini ◽

Giovanna Battipaglia ◽

Maria Chiara Manetti ◽

Piermaria Corona ◽

Manuela Romagnoli

Keyword(s):

Isotopic Composition ◽

Water Use Efficiency ◽

Water Use ◽

Tree Ring ◽

Tree Rings ◽

Minimum Temperature ◽

Growth Parameters ◽

Intrinsic Water Use Efficiency ◽

Use Efficiency ◽

Δ18o And Δ13c

Research Highlights: Chestnut trees’ (Castanea sativa Mill.) growth and their responses to climate are influenced by stand-characteristics and managements. This study highlighted that chestnut tree-ring growth is not particularly influenced by climate, while minimum temperature showed a positive relation with both intrinsic water-use efficiency (WUEi) and δ¹8O. Background and Objectives: The aim is to check the responses of chestnut trees to climate conditions and the role of stand structure and management. Materials and Methods: Stands with 12–14-year-old shoots were studied using dendrochronological and isotopic (δ18O and δ13C) approaches. Correlations with climate parameters were investigated and principal component analysis was performed using site-characteristics and tree growth parameters as variables. Results: Correlations between tree-ring width (TRW), tree-ring δ18O, and δ13C-derived intrinsic water-use efficiency (WUEi) revealed stand-dependent effects. The highest Correlations were found between climate and tree-rings’ isotopic composition. Chestnut was sensitive to high-minimum temperature in March and April, with a negative relationship with TRW and a positive relationship with WUEi. δ18O signals were not significantly different among stands. Stand thinning had a positive effect on WUEi after 1–2 years. Stand competition (indicated by shoots/stump and stumps/ha) positively influenced both WUEi and δ¹8O.

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Limitations to photosynthetic carbon gain in timberline Abies lasiocarpa seedlings during prolonged drought

Canadian Journal of Forest Research ◽

10.1139/x06-246 ◽

2007 ◽

Vol 37 (3) ◽

pp. 568-579 ◽

Cited By ~ 6

Author(s):

Daniel M. Johnson ◽

William K. Smith

Keyword(s):

Water Use Efficiency ◽

Water Use ◽

Water Status ◽

Early Summer ◽

Leaf Conductance ◽

Carbon Gain ◽

Forest Site ◽

Abies Lasiocarpa ◽

Photosynthetic Carbon ◽

Use Efficiency

Photosynthesis, water status, and associated physiological parameters were measured in chronically drought-stressed seedlings (5 years of below-average precipitation, 107 cm net deficit) of Abies lasiocarpa (Hook.) Nutt. above (treeline ecotone site, TS) and below (forest site, FS) a Rocky Mountain timberline. In contrast to normal seasonal patterns reported for timberline conifer trees, xylem water potentials were exceptionally low in early summer and remained low for the rest of the summer. Although photosynthesis was not significantly different between the two sites, early season photosynthesis was greater than late-season photosynthesis, especially at FS. Mean daily values of leaf conductance to water vapor (gwv) and transpiration (E) were also low at the beginning of summer (gwv from 0.01 mol·m–2·s–1 to 0.13 mol·m–2·s–1 and E from 0.4 μmol·m–2·s–1 to 2.9 μmol·m–2·s–1) and continued to decrease through summer (an approximate 10-fold decrease in gwv and a 2-fold to 3-fold decrease in E), which resulted in increasing water-use efficiency as summer progressed. Although the slope of instantaneous photosynthesis – intercellular CO2 concentration curves was reduced (lower carboxylation efficiency) from July to September, the relative stomatal limitation to carbon gain was less than 50% over the entire measurement period. Mean daily intercellular CO2 concentrations decreased from near ambient levels (approximately 350–360 ppm) to 290 ppm over the course of summer. Overall, nonstomatal limitations appeared to have the largest impact on photosynthetic carbon gain, although seasonal decreases in leaf conductance and a corresponding depletion of intercellular CO2 indicated that there were also significant stomatal limitations to carbon gain that resulted in a continued regulation of greater water use efficiency.

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Global tree intrinsic water use efficiency is enhanced by increased atmospheric CO2 and modulated by climate and plant functional types

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2014286118 ◽

2021 ◽

Vol 118 (7) ◽

pp. e2014286118

Author(s):

Justin M. Mathias ◽

Richard B. Thomas

Keyword(s):

Water Use Efficiency ◽

Water Use ◽

Meta Analysis ◽

Net Photosynthesis ◽

Environmental Drivers ◽

Carbon Gain ◽

Carbon And Oxygen Isotopes ◽

Functional Types ◽

Intrinsic Water Use Efficiency ◽

Use Efficiency

We conducted a meta-analysis of carbon and oxygen isotopes from tree ring chronologies representing 34 species across 10 biomes to better understand the environmental drivers and physiological mechanisms leading to historical changes in tree intrinsic water use efficiency (iWUE), or the ratio of net photosynthesis (Anet) to stomatal conductance (gs), over the last century. We show a ∼40% increase in tree iWUE globally since 1901, coinciding with a ∼34% increase in atmospheric CO2 (Ca), although mean iWUE, and the rates of increase, varied across biomes and leaf and wood functional types. While Ca was a dominant environmental driver of iWUE, the effects of increasing Ca were modulated either positively or negatively by climate, including vapor pressure deficit (VPD), temperature, and precipitation, and by leaf and wood functional types. A dual carbon–oxygen isotope approach revealed that increases in Anet dominated the observed increased iWUE in ∼83% of examined cases, supporting recent reports of global increases in Anet, whereas reductions in gs occurred in the remaining ∼17%. This meta-analysis provides a strong process-based framework for predicting changes in tree carbon gain and water loss across biomes and across wood and leaf functional types, and the interactions between Ca and other environmental factors have important implications for the coupled carbon–hydrologic cycles under future climate. Our results furthermore challenge the idea of widespread reductions in gs as the major driver of increasing tree iWUE and will better inform Earth system models regarding the role of trees in the global carbon and water cycles.

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