Effects of drought stress on growth, predawn xylem water potential (Ψ pd ), osmotic solutes (soluble sugar and proline), and stomatal conductance were assessed in two oak (Quercus cerris L. and Quercus robur L.) seedlings. Seedlings of both species were subjected to three drought treatments with the following irrigation intervals: well-watered (control: irrigation every 2-3 days), moderate drought stress (irrigation every 15 days), and severe drought stress (irrigation every 30 days). Drought-stressed seedlings of Q. cerris and Q. robur had more negative predawn xylem water potential than their well-watered seedlings. In Q. cerris, root collar diameter and root dry weights were negatively influenced by drought, while height, shoot dry weight, and root:shoot ratios were unaffected. Height and shoot dry weight of drought-stressed Q. robur were decreased, while root:shoot ratio increased. Drought caused significant decreases in stomatal conductance of both species. Q. cerris seedlings sustained higher stomatal conductance compared with Q. robur. Proline and soluble sugar increased in response to drought stress. Q. robur had a higher proline accumulation than Q. cerris. These findings suggested that the Q. cerris and Q. robur seedlings showed a drought stress adaptive mechanism either by restricting their growth or increasing root:shoot ratio or by decreasing water loss (reduced stomatal conductance) and accumulating of osmotic solutes.

Variations in the photosynthetic pigments and total carbohydrate contents of needles of different age classes (current-year, 1-year-old, 2-year-old and 3-year-old) of Pinus nigra subsp. pallasiana (Lambert) Holmboe trees in a young natural stand were investigated during the growing season. In current-year needles, total carbohydrate content was lower during June and July when the needle growth continued than in older age classes, but it was similar to other age classes in the months of August to October. Seasonal patterns of variations in total carbohydrate content were almost similar in 1-, 2-, and 3-year-old needles. Chlorophyll and carotenoid contents increased from May to June, remained relatively constant or declined slightly during summer and autumn in 1-, 2-, and 3-year-old needles. In October, the pigment content was highest in 1-year-old needles, and lowest in 3-year-old needles. Our study indicated that total carbohydrate and pigment contents were affected by needle age classes and seasons.

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Bu çalışmada farklı yetiştirme sıklıklarının 1+0 yaşlı alıç (Crataegus monogyna Jacq.) fidanlarının morfolojik özellikleri (kök boğazı çapı, fidan boyu, kök ve gövde kuru ağırlıkları, gövde/kök oranı) ile kök gelişme potansiyeli üzerindeki etkileri araştırılmıştır. Eğirdir Orman Fidanlığı'nda fidanlar arasında 3, 6, 9 ve 12 cm mesafe olacak şekilde kontrol dahil beş farklı yetiştirme sıklığı işlemi uygulanmıştır. Alıç fidanlarında farklı derecelerde uygulanan yetiştirme sıklığı, gövde:kök oranı ve kök gelişme potansiyeli hariç kök boğazı çapı, fidan boyu, gövde ve kök kuru ağırlığı üzerinde etkili bulunmuştur. En yüksek kök boğazı çapı, fidan boyu ve kuru ağırlıklar fidanlıkta 9 ve 12 cm mesafe ile yetiştirilen fidanlarda belirlenirken, en düşük değerler kontrol fidanlarında tespit edilmiştir. Eğirdir orman fidanlığı koşullarında ekimlerin fidanlar arası mesafesi 6 veya 9 cm arasında olacak şekilde seyreltilmesi daha kalın çaplı ve boylu fidan üretilmesi açısından uygun olacaktır.

Variations in seasonal responses in water relations and total carbohydrate content (TCC) in one-yearold shoots from precommercially thinned (PCT) and unthinned Anatolian black pine stands were assessed during three seasons (sampling in May, July and September) in 2015–2017. Three different treatments were established: unthinned control with 4 941 stems·ha–1 and two thinned spacing levels (2–2.5 and 3–3.5 m) where 2 133 stems·ha^–1 and 1 093 stems·ha^–1 were left, respectively. Differences in osmotic potential at turgor loss point (Ψπ_TLP) between the thinned and unthinned plots appeared only during a water shortage (September) in the second season, with the thinned stands showing lower Ψπ_TLP than the unthinned stands. Seasonal variation in terms of Ψπ_TLP was detected in the 3–3.5 m spacing trees. PCT were effective on osmotic potential at full turgor (Ψπ₁₀₀), relative water content (RWC), symplastic water at saturated point per dry weight of the shoot and dry weight fraction. In both the thinned and unthinned plots, a gradual decline was observed in RWC from May to September in all three years. Generally, although TCC was found to be higher in the 3–3.5 m spacing, control plots were also high in carbohydrates in some periods. Results reflect the ability of this species to survive in changing environments by PCT during dry periods in the three studied seasons. Although PCT has an effect on water potential components and TCC, it is not clear exactly how effective the PCT density is in osmotic adjustment.

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Özet: Küresel iklim değişikliğine bağlı olarak yaz kuraklıklarının süre uzunluğunun ve şiddetinin artması ormanları olumsuz etkileyecek olup, artan kuraklık nedeniyle ağaçların maruz kaldığı kuraklık stresinin tür bazında incelenmesi, türün verdiği tepkinin anlaşılması oldukça önemlidir. Bu çalışmada Quercus trojana P.B. Webb. fidanlarında kuraklık stresinin fizyolojik (gün ortası su potansiyeli, relatif su içeriği, gaz değişim parametreleri) ve biyokimyasal (toplam çözünebilir şeker içeriği) özellikler üzerindeki etkisi araştırılmıştır. Sera koşullarında 1+0 yaşlı fidanlara kontrol (haftada 2-3 kez sulama) ve kuraklık stresi (30 gün susuz bırakma) olmak üzere iki işlem uygulanmıştır. Kuraklık stresi ardışık iki kez tekrar edilmiştir. İki aylık stres döngüsü sonunda kuraklık stresi, gün ortası su potansiyelini, relatif su içeriğini, net fotosentez hızını, stoma iletkenliğini ve terleme oranını düşürürken, su kullanım etkinliğini ve toplam çözünebilir şeker içeriğini arttırmıştır. Çalışmada gün ortası su potansiyeli, net fotosentez hızı, stoma iletkenliği, terleme oranı ve toplam çözünebilir şeker içeriği arasında güçlü ilişkiler tespit edilmiştir.