Winter Color

What’s still green: Juniper and other conifers; rose and lilac stems; Apache plume, honeysuckle, prickly pear, yucca, iris, rock rose, sea pink, only the most well-protected hollyhock, red hot poker and mum leaves; some grasses. Someone cut high branches on trees along the main road, probably to maintain clearance for transporting house trailers and delivery vans.
What’s gray, blue or gray-green: Piñon, winterfat, saltbush, loco, snow-in-summer.
What’s red: Branches of apple and peach; stems on cholla and some shrub along the river; leaves on pinks, coral bells, beardtongues, small-leaf soapwort, pink and yellow evening primroses, some golden spur columbine, purple aster and anthemis.
What’s yellow: Globe and weeping willow branches; arborvitae and other conifers.
What’s blooming inside: South African aptenia, rochea, and kalanchoë.
Animal sightings: Small birds flit through the cottonwood.
Weather: Tuesday’s snow was gone by end of day; only ice left is on the north side of the house where if fell from the roof in December; morning temperatures in high 20's.
Weekly update: The snow is all but gone, but not the thirsty air which, no longer satisfied with drying mud, sucks water from every living thing. And some that have passed beyond.
Color intensifies in dead leaves and seed heads, when only dried pigments remain. Bare branches of globe willows and the weeping one down the road are more yellow, while chamisa and snakeweed stems are bright green. Arborvitae leaves have turned chartreuse or dark brown. More roses and beardstongues have red parts, while purple aster leaves collect morning frosts. The greys remain grey, but dead Russian thistles blacken.
These are the killing times when the days grow longer and warmer, but the mornings still fall into the twenties. The additional energy from the sun stimulates chloroplasts, the parts of plant cells that synthesize carbon dioxide (C0₂) from the air into glucose (C₆H₁₂O₆), at the very time there’s less water (H₂0) available to support the necessary chemical reactions. Unused energy provokes crises.
Conifers respond by slowing their photosynthesis. As the blue and red light-absorbing chlorophyl disappears, the yellow pigments that coexist in the chloroplast to absorb other parts of the light spectrum become obvious. Even willow and aspen barks, which maintain some level of photosynthesis during the winter for deciduous trees, reduce their metabolism.
Some non-herbaceous perennials have been producing red anthocyanin pigments (C₂₁H₂₀O₁₁) at the very time their chloroplasts are too stressed to effectively produce glucose from the same components. However, the cyanidin-3-O-glucoside flavonoid traps the mid-range of light, the greens and hotter yellows between 500 and 600nm. When Kevin Gould compared red and green leaves of saxifrage shrubs from New Zealand, he found the pigments located in the upper epidermal layer and in the mesophyll, the soft center with the chloroplasts, reduced productivity pressures by absorbing 23% of the inhaled carbon dioxide.
In optimal times, chloroplasts return the excess oxygen atoms extracted from raw materials back into the environment. The chain of chemical reactions that goes by the name photosynthesis includes many oxygen-rich intermediate stages and oxygen electron transfers that can damage cells if the process is altered slightly by poor environmental conditions. This led Hideo Yamasaki to test the possibility that anthocyanin compounds found in hibiscus flowers protect plants by acting as antioxidants.
Since, Velissarios-Phaedon Kytridis and Yiannis Manetas have looked specifically at red and green leaves from two shrubs that store the pigment near the chloroplast in the central layer and two that keep anthocyanin in the epidermis. They found the former were better able to handle laboratory-induced oxygen stress, probably because the pigment’s proximity to the chloroplast allowed it to more effectively intercept wayward oxy-radicals.
Unfortunately, his epidermal shrubs included roses. A few weeks ago several of my hybrid teas still had green leaves, and two in back had red ones. Now all that remain are green stems. Few roots have ever made it through February and March, and none with enough vigor to thrive the following summer. They may be red, but they’re not as cleverly armored against New Mexico’s late winters as the native asters and beardtongues.
Notes:Foote, Knowlton C. and Michail Schaedle. "Diurnal and Seasonal Patterns of Photosynthesis and Respiration by Stems of Populus tremuloides Michx.," Plant Physiology 58:651-655:1976.Gould, Kevin S., Thomas C. Vogelmann, Tao Han, and Michael J. Clearwater. "Profiles of Photosynthesis Within Red and Green Leaves of Quintinia serrata," Physiologia Plantarum 116:127-133:2002.Kytridis, Velissarios-Phaedon and Yiannis Manetas. "Mesophyll versus Epidermal Anthocyanins as Potential in Vivo Antioxidants: Evidence Linking the Putative Antioxidant Role to the Proximity of Oxy-radical Source," Journal of Experimental Botany 57:2203-2210:2006;their mesophyll test plants were Cistus creticus and Photinia x fraseri; the epidermal ones were Rosa sp. and Ricinus communis.Yamasaki, H, H. Uefuji, and Y. Sakihama. "Bleaching of the Red Anthocyanin Induced by Superoxide Radical," Archives of Biochemistry and Biophysics 332:183-186:1996.
Photograph: Weeping willow with yellowing bark and conifers down the road, 14 February 2009.