Because of its ability to induce contact dermatitis, the establishment and spread of poison ivy is recognized as a significant public health concern. In the current study, we quantified potential changes in the biomass and urushiol content of poison ivy as a function of incremental changes in global atmospheric carbon dioxide concentration (CO2). We also examined the rate of new leaf development following leaf removal to simulate responses to herbivory as functions of both CO2 and plant size. The experimental CO2 values (300, 400, 500. and 600 µmol mol−1) corresponded approximately to the concentration that existed during the middle of the 20th century, the current concentration and near and long-term projections for this century (2050 and 2090), respectively. Over 250 d, increasing CO2 resulted in significant increases in leaf area, leaf and stem weight, and rhizome length relative to the 300 µmol mol−1 baseline with the greatest relative increase occurring from 300 to 400 µmol mol−1. There was a nonsignificant (P = 0.18) increase in urushiol concentration in response to CO2; however, because of the stimulatory effect of CO2 on leaf biomass, the amount of urushiol produced per plant increased significantly for all CO2 above the 300 µmol mol−1 baseline. Significant increases in the rate of leaf development following leaf removal were also observed with increasing CO2. Overall, these data confirm earlier, field-based reports on the CO2 sensitivity of poison ivy but emphasize its ability to respond to even small (∼ 100 µmol mol−1) changes in CO2 above the mid-20th century carbon dioxide baseline and suggest that its rate of spread, its ability to recover from herbivory, and its production of urushiol, may be enhanced in a future, higher CO2 environment.

Most recent reviews of plant salinity response have included the concept of a nutritional disturbance as one likely mechanism by which shoot growth might be inhibited. None the less, few studies of dicotyledonous plants have presented data on nutrient transport into the most intensively growing shoot tissues. In this paper net nutrient deposition was followed for 3 d in 8 sequential, growing leaves of Lactuca sativa, which were grown either in conditions of moderate salinization, or in a growth-stimulating concentration of NaCl. The nutrient deposition was studied from 0.7 to 3.7 d following completion of stepwise salinization. This deposition was followed in immature leaves, which had attained only 1–2% of ultimate leaf mass by the completion of the study. In such young leaves development is still dominated by cell division. The transport of Ca2+ specifically to the youngest leaves was reduced by more than twice as much as was K+ transport. Transport of the other major divalent cationic nutrient, Mg2+, was not decreased for these leaves. The factors of increase for Na+ and Cl− after 3.7 d after completion of salinization averaged 152 and 62% over control levels for the three youngest leaves (for Na+ and Cl−, respectively). Though significant, these increases were only 27 and 14% as great as increases in three leaf sets of more developed growing leaves. Decreases in net K+ deposition and leaf K+ concentration were not greater for the youngest than they were for the oldest leaves. Net S deposition was reduced 44% more in younger than older growing leaves, but for most leaves not beyond the level expected due to reduced sink strength. The reduction in net P deposition also seemed more related to reduced sink strength, but was reduced to approx. 50% in both younger and more developed growing leaves. While Fe concentration was not reduced by salinization at any developmental stage, Zn2+ net transport and Zn concentration were both reduced in the two youngest leaves (57 and 70%, respectively). Given the moderate treatment imposed (Na:Ca ratio of 22) the results suggest that Ca2+ transport to the youngest leaves is probably highly sensitive to salinization of the root medium and is perhaps a key physiological response in the inhibition of leaf growth.

This study explored reflectance indices sampled with a ‘leaf reflectometer’ as measures of pigment content for leaves of contrasting light history, developmental stage and functional type (herbaceous annual versus sclerophyllous evergreen). We employed three reflectance indices: a modified normalized difference vegetation index (NDVI), an index of chlorophyll content; the red/green reflectance ratio (RRED[ratio ]RGREEN), an index of anthocyanin content; and the change in photochemical reflectance index upon dark–light conversions (ΔPRI), an index of xanthophyll cycle pigment activity. In Helianthus annuus (sunflower), xanthophyll cycle pigment amounts were linearly related to growth light environment; leaves in full sun contained approximately twice the amount of xanthophyll cycle pigments as leaves in deep shade, and at midday a larger proportion of these pigments were in the photoprotective, de-epoxidized forms relative to shade leaves. Reflectance indices also revealed contrasting patterns of pigment development in leaves of contrasting structural types (annual versus evergreen). In H. annuus sun leaves, there was a remarkably rapid increase in amounts of both chlorophyll and xanthophyll cycle pigments along a leaf developmental sequence. This pattern contrasted with that of Quercus agrifolia (coast live oak, a sclerophyllous evergreen), which exhibited a gradual development of both chlorophyll and xanthophyll cycle pigments along with a pronounced peak of anthocyanin pigment content in newly expanding leaves. These temporal patterns of pigment development in Q. agrifolia leaves suggest that anthocyanins and xanthophyll cycle pigments serve complementary photoprotective roles during early leaf development. The results illustrate the use of reflectance indices for distinguishing divergent patterns of pigment activity in leaves of contrasting light history and functional type.

Cell division was examined during leaf initiation in the slow-to-green mutant of Lolium temulentum L. to test the hypothesis that the cell cycle in the leaf primordium is a key regulator of the well characterized reduction in final leaf length in the mutant compared with that of the wild type. The cell doubling time (cdt, by colchicine method) was substantially longer in the youngest leaf primordium (YLP) of the mutant (107 h) than in the wild type (43 h) although the duration of the most rapid cell cycle (cc, by percentage labelled mitoses method) was between 18–20 h in each. As a consequence, the proportion of rapidly proliferating cells was only 20% in the mutant compared with 47% in the wild type. The size of the shoot apical meristem and the plastochron were similar between genotypes which indicates that the shoot meristem was largely buffered from the effects of the mutation. Mitotic cell area was also similar in the YLP of both genotypes. However, as the leaf elongated, mitotic cell area and interphase cell size were significantly larger in the mutant compared with the wild type. This change was coupled with a reduced number of cells per unit length of leaf in the mutant. The data are consistent in showing that the proportion of rapidly proliferating cells in the YLP (but not the rate of cell division) is a key parameter which influences growth of the leaf.