Stomatal density, anatomy and nutrient concentrations of Scots pine needles are affected by elevated CO2 and temperature

Stomatal density, anatomy and nutrient concentrations of Scots pine (Pinus sylvestris L.) needles were studied during 3 years of growth at elevated CO₂ (693 ± 30 µmol mol⁻¹), at elevated temperature (ambient +2·8–6·2 °C depending on the time of the year) and in a combination of elevated CO₂ and temperature in closed-top chambers. The treatments were started in August 1996. At elevated temperature, the needles that were grown in the first year (i.e. the 1997 cohort) were thinner, had thinner mesophyll in the abaxial side, thinner vascular cylinder and lower stomatal density than those grown at ambient temperature. The proportion of mesophyll area occupied by vascular cylinder or intercellular spaces were not changed. Lower stomatal density apparently did not lead to decreased use of water, as these needles had higher concentrations of less mobile nutrients (Ca, Mg, B, Zn and Mn), which could indicate increased total transpiration. In the 1997 and 1998 cohorts, elevation of temperature decreased concentrations of N, P, K, S and Cu. In the 1999 cohort, contradictory, higher concentrations of N and S at elevated temperature may be related to increased nutrient mineralization in the soil. Elevation of CO₂ did not affect stomatal density, needle thickness, thickness of epidermis or hypodermis, vascular cylinder or intercellular spaces. Concentrations of N, P, S and Cu decreased at elevated CO₂. Reductions were transient and most distinct in the 1997 cohort. The effects of CO₂ and temperature were in some cases interactive, which meant that in the combined treatment stomatal density decreased less than at elevated temperature, and concentrations of nutrients decreased less than expected on the basis of separate treatments, whereas the thickness of the epidermis and hypodermis decreased more than in the separate treatments. In conclusion, alterations in the anatomy and stomatal density of Scots pine needles were more distinct at elevated temperature than at elevated CO₂. Both elevated CO₂ and temperature-induced changes in nutrient concentrations that partly corresponded to the biochemical and photosynthetic alterations in the same cohorts ( Luomala et al. Plant, Cell and Environment 26, 645–660, 2003 ) Reductions in nutrient concentrations and alterations in the anatomy were transient and more evident in the needle cohort that was grown in the first treatment year.     

Effects of ultraviolet (UV) exclusion on the seasonal concentration of photosynthetic and UV-screening pigments in Scots pine needles

The effects of ultraviolet (UV) radiation on the photosynthetic and UV‐screening pigments in needles of Scots pine (Pinus sylvestris L.) saplings were studied in a UV‐exclusion field chamber experiment in northern Finland (67°N) during 2001–2002. The chambers held filters that excluded both UVB and UVA, only UVB, transmitted all UV, or lacked filters. Analyses of control needles (no filter and polyethene filter) showed that the first changes to occur in spring (end of April) was an abrupt increase in the epoxidation state (EPS) of the xanthophyll cycle pigments, likely in relation with the beginning of the photosynthetic activity. The concentration of chlorophyll, lutein, neoxanthin, α‐carotene, β‐carotene, and the size of the xanthophyll cycle pool (violaxanthin+antheraxanthin+zeaxanthin=VAZ) changed only later when needles reached their summer photosynthesis state. Exclusion of UV radiation significantly affected the xanthophyll cycle but not the other photosynthetic pigments analysed. Interestingly, the effects on xanthophylls were dependent on the sampling date. Under UVA/B‐exclusion, the EPS was increased and VAZ pool size was unchanged in April, whereas EPS remained unchanged and the VAZ pool size was reduced in May and June. The existence of two sustained and active antenna modes during winter and summer could be an explanation for the specific UV‐exclusion effect in the different season. A high‐performance liquid chromatography analysis of soluble phenolics showed that the exclusion of UVA/B radiation caused a significant effect on five compounds out of 46 studied, without affecting the concentration of the total soluble phenolics. Under UVA/B‐exclusion, the concentration of three of them (secoisolariciresinol‐glucopyranoside, two unknown) was reduced while the concentration of dicoumaroyl‐astragalin and pinosylvin monomethylether was increased compared with both controls separately. In general, the exclusion of UVA/B caused a stronger effect than the exclusion of UVB on both photosynthetic and UV screening pigments. The effects of UV radiation on xanthophyll cycle pigments were season‐specific and detectable only under stressful spring conditions (freezing temperatures and high irradiance due to snow reflection). The effect on the xanthophyll cycle could be a direct consequence of UV treatments, or an indirect consequence of the changed flavonoid composition, or a combination of both.     

Phylogenetic relationships of the tribe Operophterini (Lepidoptera, Geometridae): a case study of the evolution of female flightlessness

A molecular phylogenetic analysis was conducted in order to reconstruct the evolution of female flightlessness in the geometrid tribe Operophterini (Lepidoptera, Geometridae, Larentiinae). DNA variation in four nuclear gene regions, segments D1 and D2 of 28S rRNA, elongation factor 1α , and wingless , was examined from 22 species representing seven tribes of Larentiinae and six outgroup species. Direct optimization was used to infer a phylogenetic hypothesis from the combined sequence data set. The results obtained confirmed that Operophterini (including Malacodea ) is a monophyletic group, and Perizomini is its sister group. Within Operophterini, the genus Malacodea is the sister group to the genera Operophtera and Epirrita , which form a monophyletic group. This relationship is also supported by morphological data. The results suggest that female flightlessness has evolved independently twice: first in the lineage of Malacodea and, for the second time, in the lineage of Operophtera after its separation from the lineage of Epirrita . An alternative reconstruction (i.e. recovery of flight ability in an ancestor of Epirrita ) appears unlikely for various reasons. The similarities shared by Epirrita with a basal representative of Perizomini, Perizoma didymatum , allow the proposal of a sequence of evolutionary events that has led to flightlessness. It is likely that the transition to female flightlessness in the two lineages of Operophterini occurred after the colonization of stable forest habitats, followed by the evolution of a specific set of permissive traits, including larval polyphagy, limited importance of adult feeding, and adult flight during the cold months of the season.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 241–252.