Konvensyen Myprospec tumpu revolusi industri 4.0

Rising atmospheric concentrations of CO 2 (C a) can reduce stomatal conductance and transpiration rate in trees, but the magnitude of this effect varies considerably among experiments. The theory of optimal stomatal behaviour predicts that the ratio of photosynthesis to transpiration (instantaneous transpiration efficiency, ITE) should increase in proportion to C a. We hypothesized that plants regulate stomatal conductance optimally in response to rising C a. We tested this hypothesis with data from young Eucalyptus saligna Sm. trees grown in 12 climate-controlled whole-tree chambers for 2 years at ambient and elevated C a. Elevated C a was ambient + 240 ppm, 60% higher than ambient C a. Leaf-scale gas exchange was measured throughout the second year of the study and leaf-scale ITE increased by 60% under elevated C a, as predicted. Values of leaf-scale ITE depended strongly on vapour pressure deficit (D) in both CO 2 treatments. Whole-canopy CO 2 and H 2O fluxes were also monitored continuously for each chamber throughout the second year. There were small differences in D between C a treatments, which had important effects on values of canopy-scale ITE. However, when C a treatments were compared at the same D, canopy-scale ITE was consistently increased by 60%, again as predicted. Importantly, leaf and canopy-scale ITE were not significantly different, indicating that ITE was not scale-dependent. Observed changes in transpiration rate could be explained on the basis that ITE increased in proportion to C a. The effect of elevated C a on photosynthesis increased with rising D. At high D, C a had a large effect on photosynthesis and a small effect on transpiration rate. At low D, in contrast, there was a small effect of C a on photosynthesis, but a much larger effect on transpiration rate. If shown to be a general response, the proportionality of ITE with C a will allow us to predict the effects of C a on transpiration rate

Phosphorus deficiency inhibits growth in parallel with photosynthesis in a C3 (Panicum laxum) but not two C4 (P. coloratum and Cenchrus ciliaris) grasses

This study compared the growth and photosynthetic responses of one C 3 (Panicum laxum L.) and two C4 grasses (Panicum coloratum L. and Cenchrus ciliaris L.) to changes in soil phosphorus (P) nutrition. Plants were grown in potted soil amended with six different concentrations of P. One week before harvest, leaf elongation and photosynthetic rates and the contents of carbohydrate, P and inorganic phosphate (Pi) were measured. Five weeks after germination, plants were harvested to estimate biomass accumulation. At each soil P supply, leaf P contents were lower in the C3 (0.6-2.6 mmol Pm-2) than in the two C4 grasses (0.8-4.1 mmol Pm-2), and Pi constituted ∼40-65% of total leaf P. The P deficiency reduced leaf growth, tillering and plant dry mass to a similar extent in all three grasses. In contrast, P deficiency suppressed photosynthetic rates to a greater extent in the C 3 (50%) than the C4 grasses (25%). The foliar contents of non-structural carbohydrates were affected only slightly by soil P supply in all three species. Leaf mass per area decreased at low P in the two C4 grasses only, and biomass partitioning changed little with soil P supply. The percentage changes in assimilation rates and plant dry mass were linearly related in the C3 but not the C4 plants. Thus, P deficiency reduced growth in parallel with reductions of photosynthesis in the C3 grass, and independently of photosynthesis in the two C 4 grasses.We propose that this may be related to a greater P i requirement of C4 relative to C3 photosynthesis. Photosynthetic P use efficiency was greater and increased more with P deficiency in the C4 relative to the C3 species. The opposite was observed for whole-plant P-use efficiency. Hence, the greater P-use efficiency of C4 photosynthesis was not transferred to the whole-plant level, mainly as a result of the larger and constant leaf P fraction in the two C4 grasses

Enhanced leaf elongation rates of wheat at elevated CO₂ : is it related to carbon and nitrogen dynamics within the growing leaf blade?

This paper addresses the question of whether leaf elongation rates (LER) of monocots is controlled at high atmospheric CO₂ by nitrogen (N) and/or carbohydrate concentrations in the zones of cell division and expansion in the basal meristem of growing leaf blades. Wheat (Triticum aestivum L. cv. Hartog) was grown at high N supplies at either 360 or 700 μmol CO₂ mol⁻¹ in artificially illuminated growth chambers for 30 days prior to final harvest to determine growth parameters and chemical composition of leaf blades. We particularly focused on the spatial distribution of carbon (C), N and carbohydrate concentrations along the expanding leaf blade. Elevated CO₂ accelerated LER of expanding blade (sixth leaf blade) by 32% and this factor contributed to increase in total leaf area (18%) and shoots mass (36%). N concentrations in the expanding and last fully expanded leaf blade (LFEL) were reduced by 18% and 33%, respectively, at elevated CO₂ but soluble carbohydrate concentrations were significantly increased in the expanded leaves only. N concentrations were highest in the zones of cell division and expansion of the elongating blade but were unaffected by high CO₂ and reductions in N concentration only appeared in the cell maturing zone where division and expansion had ceased. The concentration of soluble carbohydrates was greater in the cell division and expansion than in maturation zones but was unaffected by high CO₂. C concentration was also little affected by elevated CO₂ in any zone of the blade. We conclude that greater availability of soluble carbohydrates for export from the expanded to expanding blades is the driving force for accelerated LER at elevated CO₂. It is unlikely that N concentrations limited leaf growth at high CO₂ because its concentration was unaffected by CO₂ in the zones of cell division and expansion that are most sensitive to N supply

Root and shoot factors contribute to the effect of drought on photosynthesis and growth of the C4 grass Panicum coloratum at elevated CO2 partial pressures

We examined the hypothesis that root and shoot factors influence growth responses to elevated CO2 of the C4 grass Panicum coloratum var. makarikiense cv. Bambatsi (NAD-ME malic enzyme subtype) when well watered and droughted. Plants were grown at CO2 partial pressures (pCO2) of 36 (ambient) and 100 Pa (elevated) in pot ed soil in growth chambers for 3 weeks with adequate water (day 0) before being subjected to 15 d of drought. At day 15, enhancement of shoot growth by elevated pCO2 was 70% under drought, and 44% when well watered. During the drought period, leaf CO2 assimilation rates (A) and stomatal conductance (g) (measured at 36 Pa CO2) declined after day 2, but the decline was faster at 36 Pa CO2, and by day 9, A was negligible and intercellular pCO2 had sharply increased compared with 100 Pa CO2. Changes in carbon metabolism and water relations occurred during drought and elevated CO2 generally delayed these changes. Leaf growth rates were higher at elevated CO2 at day 0 and during drought. Importantly, the decline in soil water content was slower at elevated pCO2 due to lower transpiration rates. This explained the slower decline in A, gand shoot water relations at elevated CO2 and indicates that root factors were responsible for their decline. In contrast, leaf growth rates were higher at elevated CO2, irrespective of soil water content. We conclude that both soil and leaf factors contribute to the greater growth response of P. coloratum to high CO2 under drought, and that reduced transpiration rates explains their enhanced growth

The effect of drought on plant water use efficiency of nine NAD-ME and nine NADP-ME Australian C4 grasses

We investigated the response to drought of nine NAD–malic enzyme (NAD–ME) and nine NADP–malic enzyme (NADP–ME) C4 grasses. Species were grown from seeds in potted soil in a glasshouse. Seedlings were either watered regularly or exposed to two successive drying cycles of 8–10 d each, after which plants were harvested. Under well-watered conditions, average water use efficiency (WUE; dry mass gain per unit water transpired) was similar for NAD–ME and NADP–ME C4 grasses, and ranged between 6.0 and 8.7 g dry mass kg–1 H2O. Drought enhanced WUE of most species, but to a significantly greater extent in NAD–ME (1.20-fold) than NADP–ME (1.11-fold) grasses. Inhibition of dry matter accumulation (average of 12%) and shoot elongation under drought was similar among the C4 grasses. Leaf dry matter carbon (δ13C) and oxygen (δ18O) isotope compositions were significantly different between the two C4 subtypes. Leaf δ13C averaged –13.3 and –12.2, and leaf δ18O averaged 26.0 and 26.9 in well-watered NAD–ME and NADP–ME grasses, respectively. Drought significantly reduced leaf δ13C in most C4 grasses by an average 0.5. Leaf δ18O was not significantly affected by drought, indicating that leaf δ18O does not reflect drought-induced changes in leaf transpiration of C4 grasses. In the experiment reported here, NAD–ME grasses increased their WUE under drought to a greater extent than their NADP–ME counterparts. Increased WUE of the C4 grasses under drought was primarily related to control of water loss relative to carbon gain at the leaf, rather than the plant, level

Carbon and water economy of Australian NAD-ME and NADP-ME C4 grasses

C4 grasses are grouped into three biochemical subtypes, NAD malic enzyme (NAD–ME), NADP malic enzyme (NADP–ME)and phosphoenolpyruvate carboxykinase (PCK), possessing characteristic leaf anatomy, biochemistry and physiology. This study investigates the physiological implications of these differences by comparing growth, water use efficiency (WUE, dry matter gain per unit water transpired) and gas exchange characteristics of NAD–MEand NADP–ME C4 grasses belonging to three taxonomic groups (main Chloroid assemblage, Paniceae and Andropogoneae). We grew 28 C4 grasses from seeds for 6 weeks in a glasshouse under ample water and nutrients in winter and summer. The inter-specific variation in plant dry mass (30-fold) was much greater than that in WUE (2-fold). There was no significant difference in average WUE between NAD–ME andNADP–ME grasses. Average plant dry mass and WUE were highest in the Paniceae (mostlyNADP–ME), lowest in the Andropogoneae (NADP–ME) and intermediate in the Chloroid (NAD–ME). CO2 assimilation rate (A), stomatal conductance(g) and the ratio of intercellular to ambient CO2 partial pressure (pi/p a ) were measured under standard conditions at high light. Average A and g were slightly higher in NADP–ME than NAD–ME grasses, but pi/pa was similar for the two subtypes. A did not differ between winter and summer experiments in spite of a 3-fold difference in maximal daily irradiance. Dry matter accumulation correlated positively with leaf area ratio (LAR; plant leaf area per unit plant dry mass) and specific leaf area (SLA; leaf area per unit leaf dry mass) in NAD–ME, but not NADP–ME, grasses.Variation in A (expressed on a per area basis) did not correlate with biomass accumulation or SLA. When expressed on a dry mass basis, A correlated withSLA in all C4 grasses. This study shows that there is large inter-specific variation in growth among the C4 grasses, but average WUE andA/g are similar for NAD–ME and NADP–ME species under well-watered conditions

Plant water use efficiency of 17 Australian NAD-ME and NADP-ME C₄ grasses at ambient and elevated CO₂ partial pressure

This study investigates the response to elevated CO₂ partial pressure (pCO₂) of C₄ grasses belonging to different biochemical subtypes (NAD–ME and NADP–ME), and taxonomic groups (main Chloroid assemblage, Paniceae and Andropogoneae). Seventeen C₄ grasses were grown under well-watered conditions in two glasshouses maintained at an average daily ppCO₂ of 42 (ambient) or 68 (elevated) Pa. Elevated pCO₂ significantly increased plant water-use efficiency (WUE; dry matter gain per unit water transpired) in 12 out of the 17 C₄ grasses, by an average of 33%. In contrast, only five species showed a significant growth stimulation. When all species are considered, the average plant dry mass enhancement at elevated pCO₂ was 26%. There were no significant subtype (or taxa) x pCO₂ interactions on either WUE or biomass accumulation. When leaf gas exchange was compared at growth pCO₂ but similar light and temperature, high pCO₂-grown plants had similar CO₂ assimilation rates (A) but a 40% lower stomatal conductance than their low pCO₂-grown counterparts. There were no signs of either photosynthetic or stomatal acclimation in any of the measured species. We conclude that elevated pCO₂ improved WUE primarily by reducing stomatal conductance

Vitrified plants : towards an understanding of their nature

Submerged aquatic plants and plants in tissue culture both grow in an environment that does not allow transpirational pull to be exerted on plant organs. The tissue culture environment sometimes induces abnormal growth, a phenomenon known as vitrification or hyperhydricity. The hypothesis that a water-saturated environment induces vitrification by altering the structure of plants in vitro is explored by comparing characteristics of submerged aquatic and vitrified plants. Structural similarities include limited vascular development, reduced lignification of xylem cell walls, a thinner cuticle, absence of palisade tissue in leaves, abnormal stomata and large intercellular spaces in the leaves. However, a major difference is that in aquatic plants the intercellular spaces are air filled whereas those of vitrified leaves are, at least, partially filled with water. It is speculated that lack of water movement through plants grown in water-saturated environment influences xylem development and for plants grown in vitro it may contribute to the filling of the intercellular spaces. The comparison between submerged aquatic plants and vitrified plants suggests that vitrification is primarily a plastic response of plants to the in vitro environment and can only be remedied by altering the environment, particularly the humidity